feat(api): DELETE /api/admin/tracks/{id} for M7 #372

Admin-only handler. Calls tracks.RemoveTrack with the unmonitor flag
parsed from the query string. ErrNotFound -> 404; everything else
unexpected -> 500. Lidarr-side failures during unmonitor flow as
lidarr_unmonitor_failed: true in the success envelope (non-fatal —
the file + DB delete already completed).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/server/server.go

@@ -3,6 +3,7 @@ package server
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"log/slog"
 	"net/http"
 	"strings"
@@ -23,9 +24,31 @@ import (
 	"git.fabledsword.com/bvandeusen/minstrel/internal/lidarrrequests"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/playevents"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/subsonic"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/tracks"
 	"git.fabledsword.com/bvandeusen/minstrel/web"
 )
 
+// lidarrUnmonitorAdapter wires the per-call lidarrClientFn factory pattern
+// (used elsewhere in this package so admin Lidarr config edits take effect
+// without restart) into the tracks.LidarrUnmonitorer interface that
+// internal/tracks expects. When the factory returns nil (Lidarr disabled)
+// we surface a sentinel error — tracks.Service treats UnmonitorTrack
+// failures as non-fatal, so this collapses to a `lidarr_unmonitor_failed`
+// flag in the response and the destructive part still runs.
+type lidarrUnmonitorAdapter struct {
+	fn func() *lidarr.Client
+}
+
+var errLidarrDisabled = errors.New("lidarr disabled")
+
+func (a lidarrUnmonitorAdapter) UnmonitorTrack(ctx context.Context, trackMbid, albumMbid string) error {
+	c := a.fn()
+	if c == nil {
+		return errLidarrDisabled
+	}
+	return c.UnmonitorTrack(ctx, trackMbid, albumMbid)
+}
+
 // ScanTrigger is the subset of the scanner the HTTP handler needs. Kept as an
 // interface so tests can stub it without touching the DB.
 type ScanTrigger interface {
@@ -74,7 +97,8 @@ func (s *Server) Router() http.Handler {
 		}
 		lidarrReqs := lidarrrequests.NewService(s.Pool, lidarrCfg, lidarrClientFn, nil)
 		lidarrQuar := lidarrquarantine.NewService(s.Pool, lidarrCfg, lidarrClientFn)
-		api.Mount(r, s.Pool, s.Logger, writer, s.RecommendationCfg, lidarrCfg, lidarrReqs, lidarrQuar)
+		tracksSvc := tracks.NewService(s.Pool, s.Logger, lidarrUnmonitorAdapter{fn: lidarrClientFn})
+		api.Mount(r, s.Pool, s.Logger, writer, s.RecommendationCfg, lidarrCfg, lidarrReqs, lidarrQuar, tracksSvc)
 		// /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