Add smoke tests for UOM conversions and enhance frontend UOM management

- Implemented smoke tests for UOM directionality, ensuring conversions are one-directional and correctly validated.
- Added tests for receiving and selling items in different UOMs, verifying correct quantity handling and error responses.
- Created a UOM conversions panel in the frontend to allow users to manage UOM conversions for items.
- Introduced hooks for allowed UOMs to optimize fetching and caching of UOM data for document line forms.
- Developed utility functions for consistent UOM formatting and conversion handling across the application.

Backend/smoke/uom_direction.py

@@ -0,0 +1,81 @@
+"""Smoke test — UOM conversions are one-directional, and the API says so.
+
+`UomConverter` looks up exactly one shape, `FromUom -> ToUom = item.BaseUomId`, and never
+inverts a factor. `UpdateUomConversionsAsync` used to accept *any* pair, so saving the more
+natural-reading `base -> BOX` produced a row that returned 200, appeared in the item detail
+response, and was then silently invisible to every consumer — surfacing much later as
+"no UOM conversion" 422 at GRN confirm or stage start, on an item that visibly had one.
+
+  * base -> other is rejected with 422 (the direction that used to save and then not work)
+  * other -> base is accepted
+  * a self-conversion and a base-as-source row are rejected
+  * a zero/negative factor is rejected (UomConverter divides unit cost by it)
+  * changing an item's base UOM while conversions exist is refused rather than orphaning them
+
+    python Backend/smoke/uom_direction.py
+"""
+
+from __future__ import annotations
+
+import sys
+
+from smoke_common import bootstrap
+
+
+def main():
+    c, chk, args = bootstrap(__doc__)
+    print(f"API {args.api}")
+
+    item = c.get("/items?pageSize=1&status=Active").body["items"]
+    if not item:
+        sys.exit("FATAL: no active items.")
+    item = item[0]
+    item_id, base_uom = item["itemId"], item["baseUomId"]
+
+    uoms = c.get("/uoms?pageSize=50").body["items"]
+    other = next((u["uomId"] for u in uoms if u["uomId"] != base_uom), None)
+    if other is None:
+        sys.exit("FATAL: need at least 2 UOMs.")
+    print(f"item={item_id} baseUom={base_uom} otherUom={other}")
+
+    def put(conversions):
+        return c.put(f"/items/{item_id}/uom-conversions", {"conversions": conversions})
+
+    chk.section("1. The correct direction is accepted")
+    ok = put([{"fromUom": other, "toUom": base_uom, "factor": 12}])
+    chk.status("other -> base", ok, 200)
+    if ok.status == 200:
+        chk.check("stored with the base UOM as target", ok.body["conversions"][0]["toUom"], base_uom)
+
+    chk.section("2. The reverse direction is rejected, not silently stored")
+    chk.status("base -> other", put([{"fromUom": base_uom, "toUom": other, "factor": 12}]), 422)
+
+    chk.section("3. Degenerate rows are rejected")
+    chk.status("self-conversion (other -> other)", put([{"fromUom": other, "toUom": other, "factor": 2}]), 422)
+    chk.status("zero factor", put([{"fromUom": other, "toUom": base_uom, "factor": 0}]), 422)
+    chk.status("negative factor", put([{"fromUom": other, "toUom": base_uom, "factor": -3}]), 422)
+
+    chk.section("4. Base UOM cannot be repointed while conversions exist")
+    # Restore a valid conversion first, so the guard has something to protect.
+    put([{"fromUom": other, "toUom": base_uom, "factor": 12}])
+    head = c.get(f"/items/{item_id}")
+    if head.status == 200:
+        body = head.body
+        moved = c.put(f"/items/{item_id}", {
+            "sku": body["sku"], "name": body["name"], "description": body.get("description"),
+            "categoryId": body["categoryId"], "subCategoryId": body.get("subCategoryId"),
+            "brandId": body.get("brandId"),
+            "baseUomId": other,                      # <- the repoint being guarded
+            "defaultVendorId": body.get("defaultVendorId"),
+            "stockNature": body["stockNature"], "trackingMode": body["trackingMode"],
+            "taxClass": body.get("taxClass"), "salePrice": body.get("salePrice"),
+        }, if_match=head.etag)
+        chk.status("change base UOM with conversions defined", moved, 422)
+    else:
+        chk.check("could read the item for the repoint test", head.status, 200)
+
+    return chk.finish("UOM-DIRECTION")
+
+
+if __name__ == "__main__":
+    sys.exit(main())