feat(server): playback_errors table + admin inbox endpoints

New client-reported playback-error log. Surfaces zero-duration
tracks (and future load_failed / stalled kinds) into an admin
inbox so the operator can hide / delete / re-request the
offending track.

Schema (migration 0032):
- playback_errors table with CHECK constraints on the kind +
  resolution enums (per the standing rule that new enum values
  need a migration to add)
- Partial index on unresolved rows for fast inbox lookup
- ON DELETE CASCADE from tracks + users so cleanup is automatic

Endpoints:
- POST /api/playback-errors: any signed-in user reports. Body
  validates track existence + kind whitelist; client_id required
  so support can correlate reports from the same device.
- GET /api/admin/playback-errors?resolved=false&offset=&limit=:
  admin list with join to track/album/artist for table render
  without per-row round-trips. Pagination capped at 200/page.
- POST /api/admin/playback-errors/{id}/resolve: admin marks
  resolved with a resolution enum string.

Auto-resolve on Hide/Delete/Re-request from the inbox row is
driven from the web client (two sequential calls) — keeps the
existing track-action endpoints unchanged.

internal/api/api.go

@@ -107,6 +107,10 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 			authed.Delete("/quarantine/{track_id}", h.handleUnflag)
 			authed.Get("/quarantine/mine", h.handleListMyQuarantine)
 
+			// Client-reported playback errors (zero-duration tracks,
+			// load failures). Admin-only inbox; any user can report.
+			authed.Post("/playback-errors", h.handleReportPlaybackError)
+
 			// Self-hosted in-app update channel (#397). Auth-gated to
 			// prevent anonymous bandwidth abuse on the APK stream;
 			// /apk additionally per-user rate-limited.
@@ -127,6 +131,9 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 
 				admin.Get("/quarantine", h.handleListAdminQuarantine)
 				admin.Post("/quarantine/{track_id}/resolve", h.handleResolveQuarantine)
+
+				admin.Get("/playback-errors", h.handleListAdminPlaybackErrors)
+				admin.Post("/playback-errors/{id}/resolve", h.handleResolvePlaybackError)
 				admin.Post("/quarantine/{track_id}/delete-file", h.handleDeleteQuarantineFile)
 				admin.Post("/quarantine/{track_id}/delete-via-lidarr", h.handleDeleteQuarantineViaLidarr)
 				admin.Get("/quarantine/actions", h.handleListQuarantineActions)