refactor: redesign format selection with unified list and independent audio/video picking

- Replace type/quality selection flow with unified format list (video+audio combined)
- Add independent audio/video format picking: video-only formats prompt for audio track,
  audio-only formats offer optional video addition (skip when content is audio-only)
- Fix formatKeyboard to use format IDs as callback data instead of display labels
- Remove dead mediaTypeKeyboard function
- Fix double-close panic in readProgress (caller is sole owner of updates channel)
- Add FormatString field to DownloadJob for composite format specs (e.g. '137+140')
- Change quota calculation from sum of all format sizes to max single format size
- Fix 'Delete all data' button to use danger style with proper text
- Clean up routePrefixedCallback: remove type_/quality_, add format_/secondary_ routes
- Fix back navigation to rebuild format IDs list

internal/dl/ytdlp.go

@@ -110,6 +110,7 @@ func (c *Client) GetMediaInfo(url string) (*domain.MediaInfo, error) {
 	}
 
 	langSet := make(map[string]bool)
+	var maxSize int64
 	for _, f := range info.Formats {
 		ff := c.convertFormat(f)
 		mi.Formats = append(mi.Formats, ff)
@@ -117,10 +118,11 @@ func (c *Client) GetMediaInfo(url string) (*domain.MediaInfo, error) {
 			langSet[ff.Language] = true
 			mi.Languages = append(mi.Languages, ff.Language)
 		}
-		if ff.Filesize > 0 {
-			mi.EstimatedSize += ff.Filesize
+		if ff.Filesize > maxSize {
+			maxSize = ff.Filesize
 		}
 	}
+	mi.EstimatedSize = maxSize
 
 	return mi, nil
 }
@@ -215,20 +217,25 @@ func (c *Client) StartDownload(job *domain.DownloadJob, downloadDir string) (<-c
 	formatID := job.SelectedFormat.ID
 	var args []string
 
-	// Build format string for merge
-	switch job.MediaType {
-	case domain.MediaTypeAudio:
-		args = append(args, "-f", formatID, "-x")
-		if job.Container != "" {
-			args = append(args, "--audio-format", job.Container)
-		}
-	case domain.MediaTypeVideo:
-		args = append(args, "-f", formatID)
-	case domain.MediaTypeVideoAudio:
-		// Download best video + best audio that match
-		args = append(args, "-f", formatID+"+bestaudio/best")
-		if job.Container != "" {
-			args = append(args, "--merge-output-format", job.Container)
+	// Use explicit format string if set (video+audio combination)
+	if job.FormatString != "" {
+		args = append(args, "-f", job.FormatString)
+	} else {
+		// Build format string for merge
+		switch job.MediaType {
+		case domain.MediaTypeAudio:
+			args = append(args, "-f", formatID, "-x")
+			if job.Container != "" {
+				args = append(args, "--audio-format", job.Container)
+			}
+		case domain.MediaTypeVideo:
+			args = append(args, "-f", formatID)
+		case domain.MediaTypeVideoAudio:
+			// Download best video + best audio that match
+			args = append(args, "-f", formatID+"+bestaudio/best")
+			if job.Container != "" {
+				args = append(args, "--merge-output-format", job.Container)
+			}
 		}
 	}