feat: Admin is a left rail with how many wait on you in each queue, and the Overview opens with a verdict, the queues that need you and since when, then the clear ones on one line (M503 #5605)

- GET /api/admin/summary: every admin queue (requests, reported tracks,
  playback errors, duplicates, suspect sources, missing files) with its
  count and the age of its oldest item, in one query.
- The admin layout drops the 11-tab strip for SectionRail, as Settings and
  the Collection have, with each queue's count as its badge; the counts
  refresh on each admin navigation and every 30s.
- The Overview leads with "Nothing needs you." or "N things need you.",
  lists each waiting queue with "oldest 3d ago" and a link to it, counts a
  failed library scan as a problem, and names the empty queues on one line.
  The request and quarantine previews and the stat tiles are gone; those
  queues are worked on their own pages. A failed summary says so with Try
  again instead of reading as all-clear.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/api.go

@@ -244,6 +244,8 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 				admin.Get("/lidarr/quality-profiles", h.handleListQualityProfiles)
 				admin.Get("/lidarr/metadata-profiles", h.handleListMetadataProfiles)
 				admin.Get("/lidarr/root-folders", h.handleListRootFolders)
+				// The queues that wait on an admin, for the rail and the Overview (#5605).
+				admin.Get("/summary", h.handleGetAdminSummary)
 				admin.Get("/requests", h.handleListAdminRequests)
 				admin.Post("/requests/{id}/approve", h.handleApproveRequest)
 				admin.Post("/requests/{id}/reject", h.handleRejectRequest)