Follow-ups: reference reorder, detach service_id, named-dashboard widgets

Three reusable-widget follow-up fixes:

1. Reference sort_order independently reorderable. Reordering a
   referenced widget now updates the widget_references.sort_order (per-
   dashboard), not the shared widget instance sort_order. New backend
   update_widget_reference method + PUT /api/widgets/references/{id}
   endpoint. Frontend moveInstance checks _ref_id to choose the right
   mutation (updateRef for references, saveWidget for owned).

2. Detach preserves service_id. detach_widget_reference now copies the
   original widget's service_id into the clone, so service-bound widgets
   (Grafana chart, Jellyfin activity) continue to render after detach.

3. Named dashboards support widget references. NamedDashboardPage
   fetches useWidgetReferences('named:<slug>') and renders them via
   WidgetInstanceCard alongside pinned links. 'Edit widgets' button
   opens WidgetConfigDialog with dashboardScope='named:<slug>'.

Also: removed useMemo on combinedWidgets in WidgetConfigDialog to fix
a react-hooks/preserve-manual-memoization lint error (the React Compiler
ESLint plugin couldn't verify the spread+sort memoization).

283 backend tests pass (+1 update_reference test); 128 frontend tests
pass; ruff clean; 0 lint errors.

backend/src/media_library_viewer_api/routers/widgets.py

@@ -269,6 +269,19 @@ def delete_reference(
     return {"status": "deleted"}
 
 
+@router.put("/references/{reference_id}")
+def update_reference(
+    reference_id: str,
+    sort_order: int,
+    store: SettingsStore = Depends(get_settings_store),
+) -> dict[str, Any]:
+    """Update a widget reference's sort_order (per-dashboard reordering)."""
+    try:
+        return store.update_widget_reference(reference_id, sort_order)
+    except ValueError as exc:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail=str(exc)) from exc
+
+
 @router.post("/references/{reference_id}/detach")
 def detach_reference(
     reference_id: str,

backend/src/media_library_viewer_api/services/settings_store.py

@@ -1570,6 +1570,30 @@ class SettingsStore:
         with self.connect() as conn:
             conn.execute("DELETE FROM widget_references WHERE id = ?", (reference_id,))
 
+    def update_widget_reference(self, reference_id: str, sort_order: int) -> dict[str, Any]:
+        """Update only the sort_order on a widget reference (per-dashboard reordering)."""
+        self.init_schema()
+        with self.connect() as conn:
+            row = conn.execute(
+                "SELECT * FROM widget_references WHERE id = ?",
+                (reference_id,),
+            ).fetchone()
+            if not row:
+                raise ValueError(f"Reference {reference_id} not found")
+            conn.execute(
+                "UPDATE widget_references SET sort_order = ? WHERE id = ?",
+                (sort_order, reference_id),
+            )
+        widget = self.get_widget(row["widget_id"])
+        return {
+            "id": row["id"],
+            "dashboard_scope": row["dashboard_scope"],
+            "widget_id": row["widget_id"],
+            "sort_order": sort_order,
+            "created_at": int(row["created_at"]),
+            "widget": widget,
+        }
+
     def detach_widget_reference(self, reference_id: str, dashboard_scope: str) -> dict[str, Any]:
         """Clone the referenced widget into a new standalone instance owned by the scope."""
         self.init_schema()
@@ -1583,10 +1607,11 @@ class SettingsStore:
         source = self.get_widget(row["widget_id"])
         if not source:
             raise ValueError(f"Source widget {row['widget_id']} not found")
-        # Clone: new widget with service_id=NULL (dashboard scope), same config/kind/title.
+        # Clone: copy the widget verbatim including service_id (so service-bound
+        # widgets keep working), only the id/created_at change.
         cloned = self.upsert_widget(
             {
-                "service_id": None,
+                "service_id": source.get("service_id"),
                 "widget_kind": source["widget_kind"],
                 "title": source["title"],
                 "config": source["config"],