Refactor production and stock tests to remove UOM dependency

- Updated production.spec.ts, stock-adjustments.spec.ts, and stock-transfers.spec.ts to eliminate UOM references in API seeder and test cases.
- Adjusted ApiSeeder methods to remove UOM parameters from stock receiving and production template creation.
- Revised documentation to reflect changes in UOM handling, emphasizing that stock is counted in base UOM only.
- Introduced new enums for MeasureUnit and StageQtyUnit to clarify content size and stage input quantities.
- Implemented ItemContent service to validate and normalize content sizes.
- Updated smoke tests to validate production stage inputs expressed in content units, ensuring correct consumption calculations.
- Modified frontend UOM label handling to reflect the removal of per-line UOMs in document lines.

Backend/ERPCore/Domain/Entities/BundleSaleLine.cs

@@ -12,8 +12,6 @@ public class BundleSaleLine
     public Item? Item { get; set; }
     public string Description { get; set; } = string.Empty;
     public decimal Qty { get; set; }
-    public int UomId { get; set; }
-    public Uom? Uom { get; set; }
     public int WarehouseId { get; set; }
     public Warehouse? Warehouse { get; set; }
     public decimal UnitPrice { get; set; }

Backend/ERPCore/Domain/Entities/BundleSaleTemplateLine.cs

@@ -8,8 +8,6 @@ public class BundleSaleTemplateLine
 
     public int ItemId { get; set; }
     public Item? Item { get; set; }
-    public int UomId { get; set; }
-    public Uom? Uom { get; set; }
     public int WarehouseId { get; set; }
     public Warehouse? Warehouse { get; set; }
 

Backend/ERPCore/Domain/Entities/GrnLine.cs

@@ -25,9 +25,6 @@ public class GrnLine
     public int ItemId { get; set; }
     public Item? Item { get; set; }
 
-    public int UomId { get; set; }
-    public Uom? Uom { get; set; }
-
     public int? BinId { get; set; }
     public Bin? Bin { get; set; }
 

Backend/ERPCore/Domain/Entities/Item.cs

@@ -24,6 +24,12 @@ public class Item
     public int? BrandId { get; set; }
     public Brand? Brand { get; set; }
 
+    /// <summary>
+    /// The stocking unit — the pack the item is counted in (BOTTLE, PACKET, BOX, PCS).
+    /// <b>Every</b> quantity in the system is a count of these: stock layers, the ledger,
+    /// and every document line. Nothing converts, so this is the sole meaning of a
+    /// quantity and cannot be changed once the item has stock history.
+    /// </summary>
     public int BaseUomId { get; set; }
     public Uom? BaseUom { get; set; }
 
@@ -41,6 +47,34 @@ public class Item
     /// </summary>
     public decimal? SalePrice { get; set; }
 
+    /// <summary>
+    /// How much one pack holds, as the user entered it — <c>500</c> with
+    /// <see cref="ContentUnit"/> <c>Ml</c> for a 500 ml bottle, <c>1.5</c> with <c>L</c>
+    /// for a 1.5 L one. Null (together with the other three) when the item has no
+    /// measurable content: a screw, a label, a service.
+    /// <para>
+    /// Content never affects stock — that is always a pack count. It exists so production
+    /// can express a formula in millilitres or grams and resolve it to packs
+    /// (see <c>IItemMeasure</c>).
+    /// </para>
+    /// <para>
+    /// A loose bulk item bought by weight is modelled the same way:
+    /// <c>BaseUom = KG, ContentQty = 1, ContentUnit = Kg</c> ⇒ 1000 g per stocked unit.
+    /// </para>
+    /// </summary>
+    public decimal? ContentQty { get; set; }
+    public MeasureUnit? ContentUnit { get; set; }
+
+    /// <summary>
+    /// <see cref="ContentQty"/>/<see cref="ContentUnit"/> normalised to a base unit
+    /// (L→Ml, Kg→G, both ×1000) at write time by <c>ItemContent.Normalize</c>. Server-derived
+    /// and never accepted from a client. <see cref="ContentBaseUnit"/> is therefore only ever
+    /// <see cref="MeasureUnit.Ml"/> or <see cref="MeasureUnit.G"/>.
+    /// <para>Stored rather than recomputed so every consumer reads one settled number.</para>
+    /// </summary>
+    public decimal? ContentBaseQty { get; set; }
+    public MeasureUnit? ContentBaseUnit { get; set; }
+
     public EntityStatus Status { get; set; } = EntityStatus.Active;
 
     public DateTime CreatedAt { get; set; }
@@ -50,5 +84,4 @@ public class Item
     public uint RowVersion { get; set; }
 
     public ICollection<ItemReorder> ReorderSettings { get; set; } = new List<ItemReorder>();
-    public ICollection<UomConversion> UomConversions { get; set; } = new List<UomConversion>();
 }

Backend/ERPCore/Domain/Entities/PoLine.cs

@@ -15,9 +15,6 @@ public class PoLine
     public int ItemId { get; set; }
     public Item? Item { get; set; }
 
-    public int UomId { get; set; }
-    public Uom? Uom { get; set; }
-
     public int WarehouseId { get; set; }
     public Warehouse? Warehouse { get; set; }
 

Backend/ERPCore/Domain/Entities/RunStageInput.cs

@@ -31,10 +31,14 @@ public class RunStageInput
     public int? FromRunOutputId { get; set; }
     public RunStageOutput? FromRunOutput { get; set; }
 
-    public int UomId { get; set; }
-    public Uom? Uom { get; set; }
+    /// <summary>Copied from the template input: what <see cref="PlannedQty"/> is expressed in.</summary>
+    public StageQtyUnit QtyUnit { get; set; } = StageQtyUnit.Pack;
 
-    /// <summary>Scaled at creation; per-run editable until the stage starts (FR-MFG-08, <c>409 STAGE_NOT_EDITABLE</c>).</summary>
+    /// <summary>
+    /// Scaled at creation; per-run editable until the stage starts (FR-MFG-08,
+    /// <c>409 STAGE_NOT_EDITABLE</c>). Expressed in <see cref="QtyUnit"/> — so unlike the
+    /// consumption figures below it is <b>not</b> necessarily a pack count.
+    /// </summary>
     public decimal PlannedQty { get; set; }
 
     /// <summary>

Backend/ERPCore/Domain/Entities/RunStageOutput.cs

@@ -23,10 +23,17 @@ public class RunStageOutput
 
     public string Name { get; set; } = string.Empty;
 
-    public int UomId { get; set; }
+    /// <summary>
+    /// Display label for intermediate WIP; null on the terminal output, whose unit is the
+    /// finished item's base UOM. Never converted — see <see cref="StageOutput.UomId"/>.
+    /// </summary>
+    public int? UomId { get; set; }
     public Uom? Uom { get; set; }
 
-    /// <summary>Scaled at creation; per-run editable until the stage starts.</summary>
+    /// <summary>
+    /// Scaled at creation; per-run editable until the stage starts. Every quantity on an
+    /// output is a pack count, so scrap is recorded in whole broken bottles rather than ml.
+    /// </summary>
     public decimal PlannedQty { get; set; }
 
     /// <summary>Recorded at complete. A re-complete after a rework <b>overwrites</b> this, never adds to it.</summary>

Backend/ERPCore/Domain/Entities/SalesInvoiceLine.cs

@@ -16,8 +16,6 @@ public class SalesInvoiceLine
 
     public decimal Qty { get; set; }
     public decimal FreeQty { get; set; }
-    public int UomId { get; set; }
-    public Uom? Uom { get; set; }
     public int WarehouseId { get; set; }
     public Warehouse? Warehouse { get; set; }
 

Backend/ERPCore/Domain/Entities/SalesSlipLine.cs

@@ -16,8 +16,6 @@ public class SalesSlipLine
 
     public decimal Qty { get; set; }
     public decimal FreeQty { get; set; }
-    public int UomId { get; set; }
-    public Uom? Uom { get; set; }
     public int WarehouseId { get; set; }
     public Warehouse? Warehouse { get; set; }
 

Backend/ERPCore/Domain/Entities/StageInput.cs

@@ -32,8 +32,13 @@ public class StageInput
     public int? FromOutputId { get; set; }
     public StageOutput? FromOutput { get; set; }
 
-    public int UomId { get; set; }
-    public Uom? Uom { get; set; }
+    /// <summary>
+    /// What <see cref="QtyPerBatch"/> is expressed in. Stock inputs may use
+    /// <see cref="StageQtyUnit.Content"/> (ml/g) when the item has a content size; Upstream
+    /// inputs are always <see cref="StageQtyUnit.Pack"/> — WIP is counted in the unit its
+    /// source output declares.
+    /// </summary>
+    public StageQtyUnit QtyUnit { get; set; } = StageQtyUnit.Pack;
 
     public decimal QtyPerBatch { get; set; }
 }

Backend/ERPCore/Domain/Entities/StageOutput.cs

@@ -20,8 +20,14 @@ public class StageOutput
 
     public string Name { get; set; } = string.Empty;
 
-    public int UomId { get; set; }
+    /// <summary>
+    /// Display label for intermediate work-in-progress. Required when <see cref="ItemId"/>
+    /// is null and must be null when it is set — a real item's unit is its own base UOM.
+    /// WIP never touches stock or the ledger, so this is never converted, only shown.
+    /// </summary>
+    public int? UomId { get; set; }
     public Uom? Uom { get; set; }
 
+    /// <summary>Always a pack count: of the WIP unit above, or of the item's base UOM.</summary>
     public decimal QtyPerBatch { get; set; }
 }

Backend/ERPCore/Domain/Entities/Uom.cs

@@ -1,8 +1,10 @@
 namespace ERPCore.Domain.Entities;
 
 /// <summary>
-/// Unit of Measure (FR-MD-02). Referenced as an item's base UOM and as the
-/// endpoints of a <see cref="UomConversion"/>. Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// Unit of Measure (FR-MD-02). A flat lookup, used as an item's base UOM — the pack every
+/// quantity in the system counts — and as the display label on an intermediate production
+/// output. There are no conversions between UOMs: an item is stocked in exactly one, and a
+/// differently sized pack is a different item. Model: docs/10-BACKEND-PHASE1.md Part C.1.
 /// </summary>
 public class Uom
 {

Backend/ERPCore/Domain/Entities/UomConversion.cs

@@ -1,22 +0,0 @@
-namespace ERPCore.Domain.Entities;
-
-/// <summary>
-/// Per-item conversion factor between two UOMs (FR-MD-02/03): quantity in
-/// <see cref="FromUomId"/> × <see cref="Factor"/> = quantity in <see cref="ToUomId"/>.
-/// Model: docs/10-BACKEND-PHASE1.md Part C.1.
-/// </summary>
-public class UomConversion
-{
-    public int ConversionId { get; set; }
-
-    public int ItemId { get; set; }
-    public Item? Item { get; set; }
-
-    public int FromUomId { get; set; }
-    public Uom? FromUom { get; set; }
-
-    public int ToUomId { get; set; }
-    public Uom? ToUom { get; set; }
-
-    public decimal Factor { get; set; }
-}

Backend/ERPCore/Domain/Enums/MeasureUnit.cs

@@ -0,0 +1,23 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>
+/// Unit of an item's <b>content size</b> — how much a single stocked pack holds
+/// (a 500 ml bottle, a 50 kg sack). Stored as a string in the database.
+/// <para>
+/// This is <b>not</b> a stocking unit. Stock is always counted in packs
+/// (<c>Item.BaseUomId</c>); content is a separate, optional attribute used by
+/// production to turn "2000 ml of syrup" into a pack count.
+/// </para>
+/// <para>
+/// Only <see cref="Ml"/> and <see cref="G"/> are ever stored as a <i>base</i> content
+/// unit. <see cref="L"/> and <see cref="Kg"/> are entry conveniences normalised ×1000
+/// on write by <c>ItemContent.Normalize</c>, so nothing downstream has to convert.
+/// </para>
+/// </summary>
+public enum MeasureUnit
+{
+    Ml,
+    L,
+    G,
+    Kg
+}

Backend/ERPCore/Domain/Enums/StageQtyUnit.cs

@@ -0,0 +1,22 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>
+/// What a stage input's quantity is expressed in (FR-MFG-04). Stored as a string.
+/// <para>
+/// Deliberately explicit rather than inferred from whether the item happens to have a
+/// content size: templates outlive item edits, so an inferred unit would let adding a
+/// content size to an existing item silently reinterpret every saved formula — "300"
+/// meaning 300 packs would become 300 ml.
+/// </para>
+/// </summary>
+public enum StageQtyUnit
+{
+    /// <summary>A count of the item's base UOM — bottles, packets, pieces.</summary>
+    Pack,
+
+    /// <summary>
+    /// An amount of the item's content in its base content unit (ml or g), resolved to
+    /// packs by <c>IItemMeasure</c> at stage start. Requires the item to have a content size.
+    /// </summary>
+    Content
+}