refactor: settings format picker redesign with Audio/Video sub-pickers, fix delete routing

- Replace Type/Quality settings with single Format button -> Audio/Video sub-pickers
- Each sub-picker shows format options (bitrates for audio, resolutions for video)
- Replace DefaultQuality with DefaultAudioFormat/DefaultVideoFormat in UserPreferences
- Add DB migration 002 for new preference columns
- Update repo layer SQL queries for new schema
- Update playlist flow to use new preference fields
- Fix missing deleteaccount and delaccount_ callback routing
- Add back_format routing for format picker navigation

internal/repo/store_test.go

@@ -64,7 +64,8 @@ func TestPreferences(t *testing.T) {
 	}
 
 	prefs.DefaultMediaType = domain.MediaTypeAudio
-	prefs.DefaultQuality = "best"
+	prefs.DefaultAudioFormat = "best"
+	prefs.DefaultVideoFormat = "1080p"
 	prefs.DefaultContainer = "mp3"
 	prefs.DefaultLanguage = "en"
 	if err := s.UpdatePreferences(userID, prefs); err != nil {
@@ -78,8 +79,11 @@ func TestPreferences(t *testing.T) {
 	if got.DefaultMediaType != domain.MediaTypeAudio {
 		t.Errorf("media type = %v, want Audio", got.DefaultMediaType)
 	}
-	if got.DefaultQuality != "best" {
-		t.Errorf("quality = %q, want best", got.DefaultQuality)
+	if got.DefaultAudioFormat != "best" {
+		t.Errorf("audio format = %q, want best", got.DefaultAudioFormat)
+	}
+	if got.DefaultVideoFormat != "1080p" {
+		t.Errorf("video format = %q, want 1080p", got.DefaultVideoFormat)
 	}
 	if got.DefaultContainer != "mp3" {
 		t.Errorf("container = %q, want mp3", got.DefaultContainer)