feat: add thumbnail preview, audio-only detection, /download command, tests, and bugfixes

- Add thumbnail preview with metadata (title, uploader, duration) before download
- Auto-detect audio-only sites (Spotify, SoundCloud, etc.) and skip type selection
- Add /download command for feature parity with UI button
- Fix yt-dlp defer bug: StatusFailed was overwritten to StatusCompleted
- Fix handleURLInput using editText with msgID=0 (now uses sendWithKB)
- Fix filename detection: use job ID prefix for reliable file finding
- Fix double answerCb between handleBackStep and handleDownloadPrompt
- Fix runDownload unused msgID parameter
- Fix context for download goroutine (use context.Background)
- Remove unused startWebhook h parameter
- Remove dead buildToggleKeyboard function
- Add formatBytes, formatDuration, formatLabelForDisplay tests
- Add IsAudioOnlyContent, MediaType.String tests
- Add repo integration tests (users, preferences, quotas, history, delete)
- Add cmd/bot tests (parseAllowedUsers, env helpers)
- Add edge case tests for progress parser
- Add zero/negative safety guard in formatDuration
- Add .gitea, TODO.md, opencode.json to gitignore

internal/handler/playlist.go

@@ -24,6 +24,8 @@ func (h *Handler) handlePlaylist(ctx context.Context, chatID int64, userID int64
 	}
 	h.setUserStepState(chatID, ss)
 
+	h.sendMediaPreview(ctx, chatID, info)
+
 	kb := playlistNavKeyboard(state, 0)
 	h.sendWithKB(ctx, chatID, fmt.Sprintf("Playlist: %s (%d videos)\n\nSelect videos to download:", info.Title, info.PlaylistCount), kb)
 }
@@ -169,7 +171,7 @@ func (h *Handler) handlePlaylistConfirm(ctx context.Context, chatID int64, msgID
 		}
 
 		h.setActiveJob(userID, job)
-		h.runDownload(ctx, job, 0)
+		h.runDownload(context.Background(), job)
 
 		// Wait for active job to complete
 		for {