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/domain/types.go

@@ -45,6 +45,8 @@ type Format struct {
 type MediaInfo struct {
 	URL             string
 	Title           string
+	Uploader        string
+	Thumbnail       string
 	Duration        float64
 	Formats         []Format
 	Languages       []string
@@ -54,6 +56,16 @@ type MediaInfo struct {
 	EstimatedSize   int64
 }
 
+// IsAudioOnlyContent returns true when no format carries a video stream.
+func (m *MediaInfo) IsAudioOnlyContent() bool {
+	for _, f := range m.Formats {
+		if f.HasVideo {
+			return false
+		}
+	}
+	return len(m.Formats) > 0
+}
+
 // PlaylistEntry represents a single entry in a playlist.
 type PlaylistEntry struct {
 	ID       string