Add the step-by-step fixer and library types

Each pair is a Music (Artist/Album/01 Title) or Soundtracks (Album/01 Title)
library. The new Fixer tab takes the master, then the slave, through four
reviewed steps: folder structure, album tags (optional MusicBrainz lookup;
the slave reuses the fixed master's tags), folder names and file names,
then links the two libraries. Every fix is an undoable operation.

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

internal/api/server.go

@@ -122,6 +122,11 @@ func (s *Server) Handler() http.Handler {
 				r.Get("/renames", s.handleRenamePreview)
 				r.Post("/renames", s.handleRenames)
 				r.Post("/link-identical", s.handleLinkIdentical)
+				r.Get("/fixer", s.handleFixer)
+				r.Post("/fixer/check", s.handleFixCheck)
+				r.Post("/fixer/apply", s.handleFixApply)
+				r.Put("/fixer/step", s.handleFixStep)
+				r.Post("/fixer/release", s.handleFixRelease)
 				r.Get("/tree", s.handleTree)
 				r.Post("/build", s.handleBuild)
 				r.Post("/remove", s.handleRemove)
@@ -322,13 +327,14 @@ func (s *Server) handleBrowse(w http.ResponseWriter, r *http.Request) {
 type pairView struct {
 	store.Pair
 	Naming  engine.NamingConfig `json:"naming"`
+	Fixer   engine.FixerState   `json:"fixer"`
 	Summary store.Summary       `json:"summary"`
 	Job     *engine.Job         `json:"job"`
 }
 
 func (s *Server) view(r *http.Request, p store.Pair) pairView {
 	sum, _ := s.st.Summary(r.Context(), p.ID)
-	return pairView{Pair: p, Naming: engine.NamingOf(p), Summary: sum, Job: s.eng.Job(p.ID)}
+	return pairView{Pair: p, Naming: engine.NamingOf(p), Fixer: engine.FixerStateOf(p), Summary: sum, Job: s.eng.Job(p.ID)}
 }
 
 func (s *Server) handleListPairs(w http.ResponseWriter, r *http.Request) {
@@ -367,6 +373,7 @@ type pairInput struct {
 	ApproxMatching      bool     `json:"approx_matching"`
 	ApproxThreshold     int      `json:"approx_threshold"`
 	AutoOrganize        string   `json:"auto_organize"`
+	LibraryType         string   `json:"library_type"`
 	// Naming is optional: when absent, the pair keeps its current naming.
 	Naming *engine.NamingConfig `json:"naming,omitempty"`
 }
@@ -377,6 +384,9 @@ func (in pairInput) apply(p *store.Pair) {
 	p.ScanIntervalMinutes, p.RetentionDays, p.SettleMinutes = in.ScanIntervalMinutes, in.RetentionDays, in.SettleMinutes
 	p.ApproxMatching, p.ApproxThreshold = in.ApproxMatching, in.ApproxThreshold
 	p.AutoOrganize = in.AutoOrganize
+	if in.LibraryType != "" {
+		p.LibraryType = in.LibraryType
+	}
 	if in.Naming != nil {
 		p.OrganizeConfig, _ = json.Marshal(in.Naming)
 	}
@@ -420,6 +430,8 @@ func (s *Server) handleSavePair(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 	in.apply(&p)
+	engine.ChangeLibraryType(old, &p)
+	engine.ChangeLibraryType(old, &p)
 	warns, err := s.eng.NormalizePair(&p)
 	if err != nil {
 		writeErr(w, 400, err)