Move Resos API key to central Settings service; add sidebar scrollbar styling

Removes the standalone resos_api_key from the forecasting app's own
system_config table. All credential fetches now go through
central_settings.get_resos_credentials() / get_resos_credentials_sync()
which pull from the Settings app (LXC 116) via the internal integration
endpoint — the same pattern already used for NewBook. The Resos API
Config section is removed from the forecasting Settings page; users
manage the key in the central Settings app instead.

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

backend/services/central_settings.py

@@ -98,3 +98,22 @@ def get_integration_sync(name: str) -> Optional[dict]:
 def get_newbook_credentials_sync() -> Optional[dict]:
     """Blocking variant of get_newbook_credentials for sync job contexts."""
     return _extract_newbook(get_integration_sync("newbook"))
+
+
+def _extract_resos(s: Optional[dict]) -> Optional[dict]:
+    if not s:
+        return None
+    key = s.get("api_key") or ""
+    if not key:
+        return None
+    return {"api_key": key}
+
+
+async def get_resos_credentials() -> Optional[dict]:
+    """Returns {'api_key'} from central settings, or None if not configured."""
+    return _extract_resos(await get_integration("resos"))
+
+
+def get_resos_credentials_sync() -> Optional[dict]:
+    """Blocking variant of get_resos_credentials for sync job contexts."""
+    return _extract_resos(get_integration_sync("resos"))