fix: auto-logout on 401, raise nginx timeout for nc-scan

401 Unauthorized loop:
- client.ts had no 401 handler, leaving stale expired tokens in
  localStorage. The PrivateRoute guard only checked token existence,
  so the app would render but every API call would fail silently.
- Fix: on any 401 response, clear the token and redirect to /login.

504 Gateway Timeout on nc-scan:
- nginx default proxy_read_timeout is 60s. The scan endpoint makes
  one Nextcloud request per audio file (list + metadata), which easily
  exceeds that on larger libraries.
- Fix: add a dedicated location block for nc-scan with 300s timeouts.
  General /api/ block gets explicit 60s timeouts for clarity.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/api/client.ts

@@ -26,6 +26,11 @@ async function request<T>(
   }
   const resp = await fetch(`${BASE}${path}`, { ...options, headers });
   if (!resp.ok) {
+    if (resp.status === 401) {
+      clearToken();
+      window.location.href = "/login";
+      throw new Error("Session expired");
+    }
     const error = await resp.json().catch(() => ({ detail: resp.statusText }));
     throw new Error(error.detail ?? resp.statusText);
   }