Merge feature/show-material-suppliers into the all-branches integration

Conflict in supplier_materials.py resolved by keeping HEAD's auth
(_procurement_writer) and list route while adopting the branch's UUID
parameter annotations.

frontend/src/lib/api.ts

@@ -480,6 +480,39 @@ function adaptBrandLink(raw: RawBrandLink): BrandLinkRow {
   return { id: raw.id, brand_id: raw.brand_id, brand_name: raw.brand?.name || "" };
 }
 
+// تأمین‌کنندگان متصل به یک متریال — پاسخ GET /materials/{id}/suppliers
+// Raw shape mirrors the backend dict exactly: clean supplier objects produced
+// by an atomic JOIN (select(Supplier).join(SupplierMaterial)…) — the name
+// always comes from the suppliers table, never from the material row.
+interface RawMaterialSupplier {
+  id: string;
+  name: string;
+  phone: string | null;
+  contact_person: string | null;
+  location: string | null;
+}
+
+/** Clean UI-facing type for one supplier linked to a material. */
+export interface MaterialSupplier {
+  id: string;
+  name: string;
+  phone: string | null;
+  contact_person: string | null;
+  location: string | null;
+}
+
+function adaptMaterialSupplier(raw: RawMaterialSupplier): MaterialSupplier {
+  return {
+    id: raw.id,
+    // Bound straight from the supplier object in the API response — there is
+    // no fallback, so a supplier row can never render the material's name.
+    name: raw.name,
+    phone: raw.phone,
+    contact_person: raw.contact_person,
+    location: raw.location,
+  };
+}
+
 // فایل پیوست — پاسخ بک‌اند (metadata؛ بایت‌ها از endpoint دانلود می‌آیند)
 interface RawAttachment {
   id: string;
@@ -1232,6 +1265,16 @@ export const api = {
     updateCanonicalUnit: async (id: string, canonical_unit_id: number): Promise<void> => {
       await patchData(`/materials/${id}`, { canonical_unit_id });
     },
+    // فهرست تأمین‌کننده‌های متصل به یک متریال (GET /materials/{id}/suppliers)
+    listSuppliers: async (materialId: string): Promise<MaterialSupplier[]> => {
+      // The backend returns { data: [...clean supplier objects] } from an
+      // atomic JOIN; getData<T> unwraps the envelope. No fallback data —
+      // an empty array means the material genuinely has no suppliers.
+      const raw = await getData<RawMaterialSupplier[]>(
+        `/materials/${materialId}/suppliers`,
+      );
+      return raw.map(adaptMaterialSupplier);
+    },
   },
 
   projects: {