feat: Android download page, analysis retry and a collapsible search

- /android is a public page with the latest APK, the server address to copy
  and three install steps; linked from the sign-in screen and the profile menu
- failed audio analysis can be retried from the library page, which also shows
  the most common error; the analyzer no longer burns attempts on files that
  are missing because the disk is not mounted
- the top bar search folds into a round button and slides open on click, "/"
  or Ctrl+K

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

services/api/internal/library/service.go

@@ -587,6 +587,15 @@ func (s *Service) previewOne(ctx context.Context, root, rel string, patterns []m
 }
 
 // StartScan запускает скан источника в фоне.
+// RetryAnalysis возвращает в очередь треки, которые анализатор не смог обработать (например, пока диск
+// не был смонтирован).
+func (s *Service) RetryAnalysis(ctx context.Context) (int, error) {
+	if err := requirePerm(ctx, auth.PermManageLibrary); err != nil {
+		return 0, err
+	}
+	return s.store.RetryFailedAnalysis(ctx)
+}
+
 func (s *Service) StartScan(ctx context.Context, id uuid.UUID, full bool) (Progress, error) {
 	if err := requirePerm(ctx, auth.PermManageLibrary); err != nil {
 		return Progress{}, err