Add Lieferungen section with supplier CRUD and delivery create/list.

Wire /lieferung sub-nav (list, neu, lieferanten) to supplier and delivery APIs.

src/api/ApiClient.js

@@ -71,6 +71,30 @@ export class ApiClient {
       delete: (id) => this.#empty('DELETE', `/api/brand/${enc(id)}`),
     };
 
+    this.supplier = {
+      /** GET /api/supplier → { suppliers: Supplier[] } */
+      list: () => this.#json('GET', '/api/supplier'),
+      /** POST /api/supplier → 201 { supplier } */
+      create: (body) => this.#json('POST', '/api/supplier', { body }),
+      /** PATCH /api/supplier/{id} → { supplier } */
+      update: (id, body) => this.#json('PATCH', `/api/supplier/${enc(id)}`, { body }),
+      /** DELETE /api/supplier/{id} → 204 */
+      delete: (id) => this.#empty('DELETE', `/api/supplier/${enc(id)}`),
+    };
+
+    this.delivery = {
+      /** GET /api/delivery → { deliveries: DeliverySummary[] } */
+      list: () => this.#json('GET', '/api/delivery'),
+      /** GET /api/delivery/{id} → { delivery: Delivery } */
+      get: (id) => this.#json('GET', `/api/delivery/${enc(id)}`),
+      /** POST /api/delivery → 201 { delivery: Delivery } */
+      create: (body) => this.#json('POST', '/api/delivery', { body }),
+      /** PATCH /api/delivery/{id} → { delivery: Delivery } */
+      update: (id, body) => this.#json('PATCH', `/api/delivery/${enc(id)}`, { body }),
+      /** DELETE /api/delivery/{id} → 204 */
+      delete: (id) => this.#empty('DELETE', `/api/delivery/${enc(id)}`),
+    };
+
     this.category = {
       /** GET /api/category/tree */
       tree: () => this.#json('GET', '/api/category/tree'),