feat(article): implement articlesupplier editor tab

- ApiClient: add getSuppliers, addSupplier, updateSupplier,
  orderSuppliers, deleteSupplier on article namespace
- api/index.js: expose same methods in legacy http client
- StorageManager: add #supplierWatchers Map and watchArticleSuppliers()
  backed by article-<sku> SSE signal; wired up as article.supplierWatch
- ArticleTileTab: pass article prop to ArticleSupplierTab
- ArticleSupplierDialog (new): dialog to assign / edit a supplier link
  (supplier autocomplete, Lief.-SKU, VPE, stock, EK Netto + MwSt.)
- ArticleSupplierTab: full supplier management table with reordering
  (up/down arrows → PUT /supplier/order), inline edit and delete,
  stock badge, purchase price display and empty state

src/api/index.js

@@ -329,6 +329,64 @@ export const article = {
     });
   },
 
+  /**
+   * GET /api/article/:sku/supplier → { suppliers: ArticleSupplier[] }
+   */
+  getSuppliers(sku) {
+    return http(`/api/article/${encodeURIComponent(sku)}/supplier`);
+  },
+
+  /**
+   * POST /api/article/:sku/supplier
+   * Body: { entityId, sku?, pu?, stock?, sort?, netPrice?, taxId?, taxRate? }
+   * → 201 { supplier: ArticleSupplier }
+   */
+  addSupplier(sku, body) {
+    return http(`/api/article/${encodeURIComponent(sku)}/supplier`, {
+      method: 'POST',
+      body,
+    });
+  },
+
+  /**
+   * PATCH /api/article/:sku/supplier/:id
+   * Body: { sku?, pu?, stock?, sort?, netPrice?, taxId?, taxRate? }
+   * → 200 { supplier: ArticleSupplier }
+   */
+  updateSupplier(sku, id, body) {
+    return http(
+      `/api/article/${encodeURIComponent(sku)}/supplier/${encodeURIComponent(id)}`,
+      {
+        method: 'PATCH',
+        body,
+      },
+    );
+  },
+
+  /**
+   * PUT /api/article/:sku/supplier/order
+   * Body: { ids: number[] }
+   * → 200 { ids: number[] }
+   */
+  orderSuppliers(sku, ids) {
+    return http(`/api/article/${encodeURIComponent(sku)}/supplier/order`, {
+      method: 'PUT',
+      body: { ids },
+    });
+  },
+
+  /**
+   * DELETE /api/article/:sku/supplier/:id → 204
+   */
+  deleteSupplier(sku, id) {
+    return http(
+      `/api/article/${encodeURIComponent(sku)}/supplier/${encodeURIComponent(id)}`,
+      {
+        method: 'DELETE',
+      },
+    );
+  },
+
   /**
    * GET /api/article/export.zip → application/zip (binary download)
    * `artikel.zip` = artikel.csv (semicolon-separated, Windows-1252) +