feat(api): admin endpoints for the re-acquisition policy — #2527

GET/PUT /api/admin/library/reacquisition, so every knob the sweeper
reads is editable without a restart (rule #25). Routed under /library
beside the missing-files list it governs rather than under /lidarr:
Lidarr is the mechanism, but missing files are the problem the operator
came to solve, and that is the surface they meet it on.

The payload carries one thing the settings table doesn't: the count of
albums with missing files that can never be auto-requested, because
neither they nor their artist has an MBID. Nothing can be asked of
Lidarr for a release MusicBrainz cannot name, and a feature that
silently does nothing for part of its input reads as broken -- so the
card states the number instead of leaving it to be inferred. Counted
best-effort: the settings are the point of the endpoint, and failing the
whole card because a count query hiccuped would be the wrong trade.

Range errors come back as 400 naming the field. The Go-side validation
mirrors migration 0056's CHECKs precisely so the operator reads
"grace_hours must be 1-720" rather than a constraint-violation string
surfacing as a 500.

internal/server/server.go

@@ -28,6 +28,7 @@ import (
 	"git.fabledsword.com/bvandeusen/minstrel/internal/netsettings"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/playevents"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/playlists"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/reacquisition"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/recsettings"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/subsonic"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/tags"
@@ -151,6 +152,14 @@ func (s *Server) Router() http.Handler {
 			return lidarr.NewClient(cfg.BaseURL, cfg.APIKey)
 		}
 		lidarrReqs := lidarrrequests.NewService(s.Pool, lidarrCfg, lidarrClientFn, nil)
+		// Always usable even when the load fails — it falls back to the
+		// shipped defaults rather than leaving the admin card unable to
+		// render (same posture as netsettings above).
+		reacqSettings, raErr := reacquisition.NewSettingsService(
+			context.Background(), s.Pool, s.Logger)
+		if raErr != nil {
+			s.Logger.Warn("reacquisition settings unavailable; serving defaults", "err", raErr)
+		}
 		lidarrQuar := lidarrquarantine.NewService(s.Pool, lidarrCfg, lidarrClientFn)
 		tracksSvc := tracks.NewService(s.Pool, s.Logger, lidarrUnmonitorAdapter{fn: lidarrClientFn}, s.DataDir)
 		playlistsSvc := playlists.NewService(s.Pool, s.Logger, s.DataDir)
@@ -177,7 +186,7 @@ func (s *Server) Router() http.Handler {
 				s.Logger.Error("server: recsettings boot failed", "err", err)
 			}
 		}
-		api.Mount(r, s.Pool, s.Logger, writer, s.RecommendationCfg, recSettings, lidarrCfg, lidarrReqs, lidarrQuar, tracksSvc, playlistsSvc, s.CoverEnricher, s.CoverSettings, s.TagSettings, s.LibraryScanner, s.ScanCfg, s.DataDir, smtpSender, bus, s.PlaylistScheduler, s.StreamSecret, netSettings)
+		api.Mount(r, s.Pool, s.Logger, writer, s.RecommendationCfg, recSettings, lidarrCfg, lidarrReqs, lidarrQuar, tracksSvc, playlistsSvc, s.CoverEnricher, s.CoverSettings, s.TagSettings, s.LibraryScanner, s.ScanCfg, s.DataDir, smtpSender, bus, s.PlaylistScheduler, s.StreamSecret, netSettings, reacqSettings)
 		// /api/admin/scan is the only admin route owned by the server package
 		// (it needs the Scanner). Register it as a single inline-middleware
 		// route — using r.Route("/api/admin", ...) here would create a second