feat(maintenance): show maintenance page when the API is in maintenance

The backend now answers 503 with code MAINTENANCE_MODE while maintenance is
on. Without this change a visitor got a red error toast over a broken page
client-side, and a silently empty page server-side, because fetchReq discards
the status and returns null on any failure.

- lib/maintenance.js detects the state by BOTH status 503 and the error code;
  a bare 503 can come from a reverse proxy and is not maintenance
- The axios interceptor checks it before the 401 branch, so a maintenance
  response never triggers the refresh-token path or logs the user out
- fetchReq redirects to /maintenance, with a silentMaintenance opt-out used by
  getStateInfo: that one runs inside generateMetadata and while rendering the
  maintenance page itself, where a redirect is either ineffective or loops
- redirect() works by throwing, so the try/catch blocks in the doctors,
  clinics and specialties pages now rethrow NEXT_REDIRECT instead of
  swallowing it
- clinicApi.js handles 503 too; it previously rendered maintenance as a clinic
  with zero doctors
- The page reuses the existing 404 design and is marked noindex

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

services/clinicApi.js

@@ -1,4 +1,12 @@
 // src/services/clinicApi.js
+import { redirect } from "next/navigation";
+
+import {
+  MAINTENANCE_CODE,
+  MAINTENANCE_PATH,
+  isNextRedirectError,
+} from "@/lib/maintenance";
+
 export async function getClinicDoctors(slug, params = {}) {
   try {
     const baseUrl = process.env.NEXT_PUBLIC_API_URL;
@@ -10,6 +18,14 @@ export async function getClinicDoctors(slug, params = {}) {
 
     const response = await fetch(finalUrl, { method: "GET" });
 
+    // بدون این، حالت تعمیرات به‌صورت «کلینیک بدون پزشک» رندر می‌شود که گمراه‌کننده است.
+    if (response.status === 503) {
+      const body = await response.json().catch(() => null);
+      if (body?.errors?.[0]?.code === MAINTENANCE_CODE) {
+        redirect(MAINTENANCE_PATH);
+      }
+    }
+
     if (!response.ok) {
       const text = await response.text();
       throw new Error(`HTTP ${response.status}: ${text}`);
@@ -29,6 +45,7 @@ export async function getClinicDoctors(slug, params = {}) {
         : { total_pages: 1, current: 1 },
     };
   } catch (error) {
+    if (isNextRedirectError(error)) throw error;
     console.error("❌ خطا در دریافت دکترهای کلینیک:", error);
 
     // ✅ ساختار خروجی در حالت خطا هم مثل حالت عادی