Search Deezer and MusicBrainz together; add preview clips

Search
- Albums and songs search Deezer and MusicBrainz at once and merge the
  results: duplicates keep the Deezer copy, best word matches first.
  Deezer's search misses albums it carries (Death Magnetic) and most game
  soundtracks; MusicBrainz finds them
- MusicBrainz secondary types are shown ("Soundtrack", "Live")
- Settings: Deezer + MusicBrainz (default), Deezer only, MusicBrainz only
- Search results show which service they came from

Previews
- Songs and albums get a play button (cards, rows, detail view, editor,
  and Deezer search results) for a 30-second Deezer clip; albums play
  their most popular track
- Clips are looked up fresh (Deezer URLs expire), cached 10 minutes, and
  streamed through Canon with Range support; hidden lists stay private
- Entries from MusicBrainz or added by hand are matched to Deezer on save
  so they can preview too
- "Play previews" toggle in Settings → Profile

Tests cover merging and title/artist matching; `-tags live` runs checks
against the real services.

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

internal/server/render.go

@@ -26,6 +26,7 @@ type Site struct {
 	CSSVersion   string
 	PreviewCount int
 	ShowNotes    bool
+	ShowPreviews bool
 }
 
 type pageData struct {
@@ -51,6 +52,7 @@ func (s *Server) site(ctx context.Context) Site {
 		Theme:        set[store.SettingTheme],
 		PreviewCount: 10,
 		ShowNotes:    set[store.SettingShowNotes] != "false",
+		ShowPreviews: set[store.SettingShowPreviews] != "false",
 	}
 	if site.Title == "" {
 		site.Title = DefaultTitle(site.OwnerName)