Named dashboards + pinned service links (Slice 10)

Wire up named dashboards end-to-end. The /d/:slug route (already
referenced by useDashboards-driven nav entries from slice 4) now
renders NamedDashboardPage instead of 404ing.

Backend: GET /api/dashboards/slug/:slug resolves a dashboard by slug
(404 when not found). The store method existed from slice 3; only the
router endpoint was missing.

NamedDashboardPage: renders a named dashboard's payload -- an ordered
list of inline items with a type discriminator. This slice ships
'link' items (PinnedServiceLink -> navigates to /services/:type/:id).
Full widget composition on named dashboards is a follow-up; the main
Dashboard keeps the rich WidgetConfigDialog.

PinnedServiceLink: card component (lucide icon + label) navigating to
a service page or specific tab.

Dashboard management UI on the Services page (DashboardManagementCard):
list existing dashboards with reorder/delete, create via dialog
(label -> auto-slug), add pinned service links per dashboard (label +
enabled-service dropdown). Placed on Services (the admin hub) rather
than Settings to avoid an extra nav trip.

Dashboard payload model: inline items ({ items: [{ type: 'link', label,
target }] }) -- self-contained, no separate widget-instance fetch
needed. The type discriminator allows future widget items without
breaking existing payloads.

Tests: NamedDashboardPage (renders links, not-found state),
PinnedServiceLink (renders + navigates). 112 frontend tests pass (+6);
271 backend tests pass (no regression); lint/build green both sides.

Refs openspec/changes/services-as-hub-ia/ (spec R5, tasks slice 10).

backend/src/media_library_viewer_api/routers/dashboards.py

@@ -17,6 +17,14 @@ def list_dashboards(store: SettingsStore = Depends(get_settings_store)) -> list[
     return [NamedDashboard(**row) for row in rows]
 
 
+@router.get("/slug/{slug}")
+def get_dashboard_by_slug(slug: str, store: SettingsStore = Depends(get_settings_store)) -> NamedDashboard:
+    row = store.get_dashboard_by_slug(slug)
+    if not row:
+        raise HTTPException(status_code=404, detail="Dashboard not found")
+    return NamedDashboard(**row)
+
+
 @router.post("")
 def create_dashboard(body: NamedDashboardInput, store: SettingsStore = Depends(get_settings_store)) -> NamedDashboard:
     row = store.upsert_dashboard(body.model_dump())