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

cmd/bot/main.go

@@ -74,7 +74,7 @@ func main() {
 	defer cancel()
 
 	if url := os.Getenv("BOT_WEBHOOK_URL"); url != "" {
-		startWebhook(ctx, b, h, url)
+		startWebhook(ctx, b, url)
 	} else {
 		if _, err := b.DeleteWebhook(ctx, &tgbot.DeleteWebhookParams{}); err != nil {
 			slog.Warn("failed to delete webhook", "error", err)