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/integrations/registry.ts

@@ -10,6 +10,8 @@ import { PrometheusMetricWidget } from "../widgets/PrometheusMetricWidget";
 import { QbittorrentActiveTorrentsWidget } from "../widgets/QbittorrentActiveTorrentsWidget";
 import { QbittorrentSpeedWidget } from "../widgets/QbittorrentSpeedWidget";
 import { QbittorrentTotalsWidget } from "../widgets/QbittorrentTotalsWidget";
+import { RequestStatWidget } from "../widgets/RequestStatWidget";
+import { RequestsOverviewWidget } from "../widgets/RequestsOverviewWidget";
 import { SshTaskWidget } from "../widgets/SshTaskWidget";
 import { StaticWidget } from "../widgets/StaticWidget";
 import type {
@@ -252,6 +254,41 @@ export const SERVICE_REGISTRY: Record<string, ServiceBinding> = {
 				configSchema: { type: "object", properties: {}, required: [] },
 				component: JellyfinNowPlayingWidget,
 			},
+			{
+				kind: "stat",
+				name: "Request stat",
+				description: "A single Jellyseerr request statistic (e.g. pending requests).",
+				refreshIntervalMs: 60_000,
+				defaultConfig: { stat: "pending" },
+				configSchema: {
+					type: "object",
+					properties: {
+						stat: {
+							type: "string",
+							enum: [
+								"total",
+								"pending",
+								"approved",
+								"declined",
+								"processing",
+								"available",
+							],
+							description: "Which request count to display",
+						},
+					},
+					required: [],
+				},
+				component: RequestStatWidget,
+			},
+			{
+				kind: "stats_overview",
+				name: "Requests overview",
+				description: "All Jellyseerr request stats plus a recent-requests list.",
+				refreshIntervalMs: 60_000,
+				defaultConfig: {},
+				configSchema: { type: "object", properties: {}, required: [] },
+				component: RequestsOverviewWidget,
+			},
 		],
 	},
 	nextcloud: {