feat(jellyseer): stat widgets + rich Requests tab (slice 3/3)

Frontend for Jellyseerr request stats, reusing the generic stat abstraction.

- api/jellyseerr.ts + hooks/useJellyseer.ts: fetchJellyseerrStats +
  useJellyseerrStats (polls /api/jellyseerr/stats, no-retry; shares the backend
  cache with the widgets).
- Two reusable widgets backed by the stat/stats_overview kinds:
  - RequestStatWidget: a single selected stat (big value + label).
  - RequestsOverviewWidget: a MetricCard grid of all stats + a recent-requests
    list with status/media-status badges.
- registry.ts: Jellyfin gains `stat` (a dropdown over
  total/pending/approved/declined/processing/available — the "extract one stat
  into a widget" affordance, rendered as a Select via the existing enum UI) and
  `stats_overview` widget kinds, wired to the new components.
- RequestsTab rewritten: live stats grid (6 counts) + recent-requests list +
  a hint to pin individual stats via the Request stat widget. Reads
  jellyseerr_url from config and the now-secret jellyseerr_api_key from
  secrets_set.

Tests: RequestStatWidget + RequestsOverviewWidget rendering/error; RequestsTab
not-configured CTA, configured stats grid, and error states. 184/184 frontend
tests pass; tsc + ESLint clean.

frontend/src/api/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: frontend/src/api
 
 ## role
-Frontend API client layer that centralizes all HTTP communication with backend services using typed, token-authenticated request functions.
+Centralized API client layer providing typed functions for frontend communication with various backend services and external integrations.
 ## parent
 index: frontend/src/.pi-map.index.md
 map: frontend/src/.pi-map.md
@@ -13,6 +13,7 @@ map: frontend/src/.pi-map.md
 - backups.ts
 - client.ts
 - dashboards.ts
+- jellyseerr.ts
 - services.ts
 - shared.ts
 - widgets.ts