feat: add language selection combobox and update TTS dialog for improved language handling

src/lib/api/services/tts.ts

@@ -98,6 +98,11 @@ export const ttsService = {
           bValue = new Date(bValue as string).getTime()
         }
 
+        // Handle null values
+        if (aValue === null && bValue === null) return 0
+        if (aValue === null) return 1
+        if (bValue === null) return -1
+
         const comparison = aValue > bValue ? 1 : -1
         return params.sort_order === 'asc' ? comparison : -comparison
       })