fix: split HTTP connect/read timeouts (Jellyfin build + qBit stats)

Every HTTP client passed an integer timeout to requests, applying the same
value to BOTH connect and read phases. A slow Jellyfin /Items page or qBit
/sync/maindata blew through the 10s read budget → ReadTimeoutError. Split
into a (connect=5s, read=60s default) tuple via shared http_timeout() helper.
The media index build worker uses a 180s read floor. Existing services with
low timeout_seconds benefit from bumping to 60+.

backend/src/media_library_viewer_api/integrations/prometheus.py

@@ -31,7 +31,7 @@ def test_connection(
         grafana_url = str(config.get("grafana_url") or "").rstrip("/")
         api_key = str(secrets.get("grafana_api_key") or "")
         datasource_uid = str(config.get("datasource_uid") or "prometheus")
-        timeout = int(config.get("timeout_seconds") or 10)
+        timeout = int(config.get("timeout_seconds") or 60)
         if not grafana_url:
             return TestResult(ok=False, detail="Grafana gateway URL is required.")
         if not api_key:
@@ -73,7 +73,7 @@ class PrometheusConfig(ServiceConfigBase):
 
     grafana_url: ServiceBaseUrl
     datasource_uid: str = "prometheus"
-    timeout_seconds: int = 10
+    timeout_seconds: int = 60
 
 
 class PrometheusMetricWidgetConfig(WidgetConfigBase):