feat: collapse days hides map markers, Immich test-before-save (#216)

Map markers:
- Collapsing a day in the sidebar hides its places from the map
- Places assigned to multiple days only hide when all days collapsed
- Unplanned places always stay visible

Immich settings:
- New POST /integrations/immich/test endpoint validates credentials
  without saving them
- Save button disabled until test connection passes
- Changing URL or API key resets test status
- i18n: testFirst key for all 12 languages

server/src/routes/immich.ts

@@ -73,6 +73,24 @@ router.get('/status', authenticate, async (req: Request, res: Response) => {
   }
 });
 
+// Test connection with provided credentials (without saving)
+router.post('/test', authenticate, async (req: Request, res: Response) => {
+  const { immich_url, immich_api_key } = req.body;
+  if (!immich_url || !immich_api_key) return res.json({ connected: false, error: 'URL and API key required' });
+  if (!isValidImmichUrl(immich_url)) return res.json({ connected: false, error: 'Invalid Immich URL' });
+  try {
+    const resp = await fetch(`${immich_url}/api/users/me`, {
+      headers: { 'x-api-key': immich_api_key, 'Accept': 'application/json' },
+      signal: AbortSignal.timeout(10000),
+    });
+    if (!resp.ok) return res.json({ connected: false, error: `HTTP ${resp.status}` });
+    const data = await resp.json() as { name?: string; email?: string };
+    res.json({ connected: true, user: { name: data.name, email: data.email } });
+  } catch (err: unknown) {
+    res.json({ connected: false, error: err instanceof Error ? err.message : 'Connection failed' });
+  }
+});
+
 // ── Browse Immich Library (for photo picker) ────────────────────────────────
 
 router.get('/browse', authenticate, async (req: Request, res: Response) => {