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/keyboard.go

@@ -128,40 +128,6 @@ func progressKeyboard(pct float64, speed, eta string) models.InlineKeyboardMarku
 	}
 }
 
-// buildToggleKeyboard creates an on/off picker for a boolean setting.
-// Matches worktimeBot's pattern with "> " prefix for the current selection.
-func buildToggleKeyboard(userID int64, setting, label string, st *domain.UserPreferences) (string, models.InlineKeyboardMarkup) {
-	current := false
-	switch setting {
-	case "quality":
-		current = st.DefaultQuality == "best"
-	case "container":
-		current = st.DefaultContainer == "mp4"
-	}
-	options := []struct {
-		label string
-		data  string
-		value bool
-	}{
-		{"Enabled", setting + "_enable", true},
-		{"Disabled", setting + "_disable", false},
-	}
-	rows := [][]models.InlineKeyboardButton{}
-	for _, opt := range options {
-		l := opt.label
-		if opt.value == current {
-			l = "> " + l
-		}
-		rows = append(rows, []models.InlineKeyboardButton{
-			{Text: l, CallbackData: opt.data},
-		})
-	}
-	rows = append(rows, []models.InlineKeyboardButton{
-		{Text: "Back to Settings", CallbackData: "back_settings"},
-	})
-	return label + ":", models.InlineKeyboardMarkup{InlineKeyboard: rows}
-}
-
 // playlistNavKeyboard builds the paginated navigation for playlist selection.
 func playlistNavKeyboard(state *domain.PlaylistState, selectedCount int) models.InlineKeyboardMarkup {
 	totalPages := (len(state.Entries) + state.PerPage - 1) / state.PerPage