sku and item fix

docs/11-BACKEND-PHASE1.md

@@ -359,26 +359,39 @@ Requires `If-Match`. → **200 OK**; `412` on mismatch; `409` on duplicate name.
 Query: `q`, `status` (`Active|Inactive`), + paging. Pass `status=Active` for selectable rows.
 **200 OK**
 ```json
-{ "items": [ { "itemTypeId": 1, "name": "Color", "status": "Active",
+{ "items": [ { "itemTypeId": 1, "name": "Color", "isMeasurable": false, "status": "Active",
       "createdAt": "2026-07-16T09:00:00Z", "updatedAt": null },
-             { "itemTypeId": 2, "name": "Size", "status": "Active",
+             { "itemTypeId": 2, "name": "Size", "isMeasurable": false, "status": "Active",
       "createdAt": "2026-07-16T09:00:00Z", "updatedAt": null } ],
   "pagination": { "page": 1, "pageSize": 20, "totalItems": 2, "totalPages": 1 } }
 ```
-`Color` and `Size` are seeded on first start; users add their own (e.g. `Material`).
+`Color` and `Size` are seeded on first start, both with `isMeasurable: false`; users add their own
+(e.g. `Material`, or a `Pack Size` with `isMeasurable: true`).
+
+**`isMeasurable`** (added 2026-08-11) marks a dimension whose values are content *measurements*
+(500 ml, 1 L) rather than plain labels. The item builder then captures a number + unit per value
+and writes that pair to each generated item's `contentQty`/`contentUnit`, instead of copying one
+form-level pair into every variant — which is what makes "Coca-Cola in 500 ml / 1 L / 250 ml"
+three correctly sized items. It is why an apparel `Size` (S/M/L) can stay plain text while a
+`Volume` dimension carries units. The server never reads it when writing an item: each item's
+pair is still validated and normalised on its own.
 
 #### `GET /item-types/{itemTypeId}` → **200 OK** (+ `ETag`); `404` if absent.
 
 #### `POST /item-types`
 ```json
-{ "name": "Material" }
+{ "name": "Pack Size", "isMeasurable": true }
 ```
 **201 Created** — `Location: /api/v1/item-types/3` → the `ItemTypeDto`. `409` if the name exists.
-Callable from the item builder's inline "+" as well as the admin screen.
+`isMeasurable` is optional and defaults to `false`. Callable from the item builder's inline "+"
+as well as the admin screen.
 
 #### `PUT /item-types/{itemTypeId}`
 Requires `If-Match`. → **200 OK**; `412` on mismatch; `409` on duplicate name.
 **Renaming does not touch existing items** — nothing joins back to this row.
+`isMeasurable` is **nullable in the request body and preserved when omitted**: a plain `bool`
+would bind an absent property as `false`, so a name-only PUT — which is what the admin screen
+used to send — would clear the flag on every rename.
 
 #### `PATCH /item-types/{itemTypeId}/status` → **204 No Content**. Deactivate, never delete (FR-MD-08).