feat(jellyseer): stats backend — provider, stat widgets, router (slice 1/3)

Groundwork for Jellyseerr request stats in the Jellyfin service, behind a
small reusable abstraction so future stats services (Sonarr/Radarr) reuse it.

Backend:
- JellyseerrClient.request_count() -> /api/v1/request/count (normalized
  total/pending/approved/declined/processing/available) and recent_requests()
  -> /api/v1/request mapped to {name,type,status,media_status,created_at}
  with numeric status enums labelled.
- widgets/stats_provider.py: StatsProvider protocol + registry keyed by
  service_type (StatValue/StatsResult). A thin generic interface.
- widgets/jellyseerr_stats.py: JellyseerrStatsProvider registered for the
  Jellyfin service; reuses one authenticated client per service (lru_cache) and
  caches the StatsResult for ~10s under a lock, so multiple widgets + the tab
  collapse onto one Jellyseerr fetch (same lesson as the qBittorrent client).
  Accepts jellyseerr_api_key from secrets OR config during the upcoming
  config->secret migration.
- Jellyfin service gains two widget kinds: `stat` (a Literal selector over the
  six stats — the "extract one value into a widget" affordance) and
  `stats_overview` (all stats + recent list).
- widgets router routes widget_kind in {stat, stats_overview} to a generic
  StatsWidgetSource (dispatches to the service type's provider), independent of
  service type.
- new /api/jellyseerr/stats router endpoint for the Requests tab (resolves the
  Jellyfin service by id or first-enabled; shares the provider cache).

Tests: provider normalization, not-configured, TTL caching; stat selector +
overview + unknown-stat widget dispatch; 7 new tests. 400/400 backend pass;
ruff clean.

backend/src/media_library_viewer_api/clients/jellyseerr.py

@@ -15,6 +15,23 @@ from media_library_viewer_api.clients.http_timeout import DEFAULT_READ_TIMEOUT,
 
 logger = logging.getLogger(__name__)
 
+# Jellyseerr numeric status enums (see Overseerr/Jellyseerr source).
+_REQUEST_STATUS: dict[int, str] = {1: "pending", 2: "approved", 3: "declined"}
+_MEDIA_STATUS: dict[int, str] = {
+    1: "unknown",
+    2: "pending",
+    3: "processing",
+    4: "partially_available",
+    5: "available",
+}
+
+
+def _label(value: Any, table: dict[int, str]) -> str:
+    try:
+        return table.get(int(value), str(value))
+    except (TypeError, ValueError):
+        return str(value) if value is not None else ""
+
 
 class JellyseerrClient:
     """Small wrapper around the Jellyseerr REST API."""
@@ -136,3 +153,45 @@ class JellyseerrClient:
 
         logger.info("Jellyseerr returned %s users", len(results))
         return results
+
+    def request_count(self) -> dict[str, int]:
+        """Return normalized request counts from /api/v1/request/count.
+
+        Jellyseerr reports pending/approved/declined/processing/available/total.
+        Missing keys default to 0 so callers can rely on a stable shape.
+        """
+        payload = self.get("/request/count")
+        if not isinstance(payload, dict):
+            payload = {}
+        keys = ("total", "pending", "approved", "declined", "processing", "available")
+        counts = {k: int(payload.get(k) or 0) for k in keys}
+        logger.info(
+            "Jellyseerr request counts total=%s pending=%s processing=%s",
+            counts["total"],
+            counts["pending"],
+            counts["processing"],
+        )
+        return counts
+
+    def recent_requests(self, take: int = 20) -> list[dict[str, Any]]:
+        """Return the most recently modified requests, lightly mapped."""
+        take = max(1, min(int(take), 100))
+        payload = self.get("/request", sort="modified", skip=0, take=take)
+        if not isinstance(payload, dict):
+            return []
+        results = payload.get("results") or []
+        items = [r for r in results if isinstance(r, dict)] if isinstance(results, list) else []
+        mapped: list[dict[str, Any]] = []
+        for r in items:
+            media = r.get("media") or {}
+            mapped.append(
+                {
+                    "id": r.get("id"),
+                    "type": r.get("type"),
+                    "name": r.get("title") or media.get("title") or media.get("name") or "—",
+                    "status": _label(r.get("status"), _REQUEST_STATUS),
+                    "media_status": _label((media or {}).get("status"), _MEDIA_STATUS),
+                    "created_at": r.get("createdAt"),
+                }
+            )
+        return mapped