Add album view and bulk actions to Review

The Review list can now be grouped by album (disc folders folded in),
showing per-album counts of upgrades, identical files, downgrades and
approximate matches. Whole albums or individual songs can be selected and
linked, promoted, ignored or un-ignored in one action.

Every bulk action is previewed server-side first: how many songs will be
processed, which are skipped and why, and warnings with examples for
downgrades, approximate matches, duration mismatches, folder moves and
renames. Downgrades are excluded unless explicitly included, and
replacing master files requires an acknowledgement. Link and promote run
as a background job that re-plans each song and uses the normal
single-item operation, so all preflight checks still apply. IDs from
another pair are refused and duplicates are ignored.

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

internal/api/server.go

@@ -84,6 +84,9 @@ func (s *Server) Handler() http.Handler {
 				r.Post("/job/cancel", s.handleCancelJob)
 				r.Get("/matches", s.handleMatches)
 				r.Get("/export.csv", s.handleExport)
+				r.Get("/groups", s.handleGroups)
+				r.Post("/bulk/preview", s.handleBulkPreview)
+				r.Post("/bulk", s.handleBulk)
 				r.Post("/link-identical", s.handleLinkIdentical)
 				r.Get("/tree", s.handleTree)
 				r.Post("/build", s.handleBuild)
@@ -172,7 +175,8 @@ func opErr(w http.ResponseWriter, err error) {
 	case errors.Is(err, engine.ErrBusy), errors.Is(err, engine.ErrDowngrade), errors.Is(err, engine.ErrConfirm),
 		errors.Is(err, fsops.ErrChanged), errors.Is(err, fsops.ErrExists):
 		writeErr(w, 409, err)
-	case errors.Is(err, fsops.ErrOutsideRoot), errors.Is(err, fsops.ErrNotRegular), errors.Is(err, fsops.ErrCrossDevice):
+	case errors.Is(err, fsops.ErrOutsideRoot), errors.Is(err, fsops.ErrNotRegular), errors.Is(err, fsops.ErrCrossDevice),
+		errors.Is(err, engine.ErrInvalidBulk):
 		writeErr(w, 400, err)
 	default:
 		writeErr(w, 500, err)
@@ -418,7 +422,13 @@ func (s *Server) handleMatches(w http.ResponseWriter, r *http.Request) {
 	q := r.URL.Query()
 	limit, _ := strconv.Atoi(q.Get("limit"))
 	offset, _ := strconv.Atoi(q.Get("offset"))
-	ms, total, err := s.st.Matches(r.Context(), id, store.MatchFilter{Status: q.Get("status"), Query: q.Get("q"), Limit: limit, Offset: offset})
+	var ids []int64
+	for _, part := range strings.Split(q.Get("ids"), ",") {
+		if n, err := strconv.ParseInt(strings.TrimSpace(part), 10, 64); err == nil && n > 0 {
+			ids = append(ids, n)
+		}
+	}
+	ms, total, err := s.st.Matches(r.Context(), id, store.MatchFilter{Status: q.Get("status"), Query: q.Get("q"), IDs: ids, Limit: limit, Offset: offset})
 	if err != nil {
 		writeErr(w, 500, err)
 		return
@@ -567,3 +577,60 @@ func (s *Server) handlePurge(w http.ResponseWriter, r *http.Request) {
 	}
 	writeJSON(w, 200, map[string]any{"ok": true})
 }
+
+// ---- album grouping and bulk actions ----
+
+func (s *Server) handleGroups(w http.ResponseWriter, r *http.Request) {
+	id, _ := idParam(r)
+	q := r.URL.Query()
+	groups, err := s.eng.Groups(r.Context(), id, store.MatchFilter{Status: q.Get("status"), Query: q.Get("q")})
+	if err != nil {
+		writeErr(w, 500, err)
+		return
+	}
+	writeJSON(w, 200, groups)
+}
+
+type bulkBody struct {
+	engine.BulkOptions
+	IDs []int64 `json:"ids"`
+}
+
+func (s *Server) handleBulkPreview(w http.ResponseWriter, r *http.Request) {
+	id, _ := idParam(r)
+	var b bulkBody
+	if !readJSON(w, r, &b) {
+		return
+	}
+	p, err := s.eng.PreviewBulk(r.Context(), id, b.IDs, b.BulkOptions)
+	if err != nil {
+		writeErr(w, 400, err)
+		return
+	}
+	writeJSON(w, 200, p)
+}
+
+func (s *Server) handleBulk(w http.ResponseWriter, r *http.Request) {
+	id, _ := idParam(r)
+	var b bulkBody
+	if !readJSON(w, r, &b) {
+		return
+	}
+	switch b.Action {
+	case engine.BulkIgnore, engine.BulkUnignore:
+		n, err := s.eng.ApplyIgnore(r.Context(), id, b.IDs, b.BulkOptions)
+		if err != nil {
+			writeErr(w, 400, err)
+			return
+		}
+		writeJSON(w, 200, map[string]any{"changed": n})
+	default:
+		j, err := s.eng.StartBulk(id, b.IDs, b.BulkOptions)
+		if err != nil {
+			opErr(w, err)
+			return
+		}
+		s.log.Info("bulk action started", "pair", id, "action", b.Action, "songs", len(b.IDs), "allow_downgrade", b.AllowDowngrade)
+		writeJSON(w, 202, j)
+	}
+}