feat: add 'Ask' quality option, language auto-select, and m4a audio remux

- Add 'ask' option to audio/video quality settings (stored as '' in DB)
- Auto-select when both media type AND quality are set; show filtered
  format picker when quality is Ask
- Auto-skip language picker when user has a matching language preference
- Remux audio-only downloads to m4a instead of webm for Telegram compat
- Update README to document the new flow and m4a audio output

internal/handler/settings.go

@@ -14,11 +14,11 @@ import (
 func (h *Handler) buildSettingsKeyboard(userID int64, prefs *domain.UserPreferences) (string, models.InlineKeyboardMarkup) {
 	audioFmt := prefs.DefaultAudioFormat
 	if audioFmt == "" {
-		audioFmt = "best"
+		audioFmt = "ask"
 	}
 	videoFmt := prefs.DefaultVideoFormat
 	if videoFmt == "" {
-		videoFmt = "best"
+		videoFmt = "ask"
 	}
 	langLabel := prefs.DefaultLanguage
 	if langLabel == "" {
@@ -101,11 +101,13 @@ func (h *Handler) buildQualityAudioVideoPicker(prefs *domain.UserPreferences) (s
 }
 
 func (h *Handler) buildAudioQualityPicker(prefs *domain.UserPreferences) (string, models.InlineKeyboardMarkup) {
-	bitrates := []string{"best", "128k", "192k", "256k", "320k"}
+	bitrates := []string{"ask", "best", "128k", "192k", "256k", "320k"}
 	rows := [][]models.InlineKeyboardButton{}
 	for _, b := range bitrates {
 		label := b
-		if b == prefs.DefaultAudioFormat {
+		if b == "ask" && prefs.DefaultAudioFormat == "" {
+			label = "> " + label
+		} else if b != "ask" && b == prefs.DefaultAudioFormat {
 			label = "> " + label
 		}
 		rows = append(rows, []models.InlineKeyboardButton{
@@ -119,12 +121,14 @@ func (h *Handler) buildAudioQualityPicker(prefs *domain.UserPreferences) (string
 }
 
 func (h *Handler) buildVideoQualityPicker(prefs *domain.UserPreferences) (string, models.InlineKeyboardMarkup) {
-	resolutions := []string{"best", "2160p", "1440p", "1080p", "720p", "480p", "360p"}
+	resolutions := []string{"ask", "best", "2160p", "1440p", "1080p", "720p", "480p", "360p"}
 	rows := [][]models.InlineKeyboardButton{}
 	row := []models.InlineKeyboardButton{}
 	for i, r := range resolutions {
 		label := r
-		if r == prefs.DefaultVideoFormat {
+		if r == "ask" && prefs.DefaultVideoFormat == "" {
+			label = "> " + label
+		} else if r != "ask" && r == prefs.DefaultVideoFormat {
 			label = "> " + label
 		}
 		row = append(row, models.InlineKeyboardButton{
@@ -220,9 +224,15 @@ func (h *Handler) handleSettingsSet(ctx context.Context, chatID int64, msgID int
 		}
 		changed = true
 	case "audioquality":
+		if value == "ask" {
+			value = ""
+		}
 		prefs.DefaultAudioFormat = value
 		changed = true
 	case "videoquality":
+		if value == "ask" {
+			value = ""
+		}
 		prefs.DefaultVideoFormat = value
 		changed = true
 	case "language":