Refactor ProfileForm to support draft state management and improve file handling

- Introduced functionality to save and restore form state as a draft when creating a new voice profile.
- Added helper functions for converting files to and from base64 format to facilitate file handling.
- Updated the API types to use a more flexible LanguageCode type for language parameters.
- Enhanced the UI store to manage profile form drafts, improving user experience during profile creation.

app/src/lib/api/client.ts

@@ -1,4 +1,5 @@
 import { useServerStore } from '@/stores/serverStore';
+import type { LanguageCode } from '@/lib/constants/languages';
 import type {
   VoiceProfileCreate,
   VoiceProfileResponse,
@@ -254,7 +255,7 @@ class ApiClient {
   }
 
   // Transcription
-  async transcribeAudio(file: File, language?: 'en' | 'zh'): Promise<TranscriptionResponse> {
+  async transcribeAudio(file: File, language?: LanguageCode): Promise<TranscriptionResponse> {
     const formData = new FormData();
     formData.append('file', file);
     if (language) {

app/src/lib/api/types.ts

@@ -1,9 +1,10 @@
 // API Types matching backend Pydantic models
+import type { LanguageCode } from '@/lib/constants/languages';
 
 export interface VoiceProfileCreate {
   name: string;
   description?: string;
-  language: 'en' | 'zh';
+  language: LanguageCode;
 }
 
 export interface VoiceProfileResponse {
@@ -29,7 +30,7 @@ export interface ProfileSampleResponse {
 export interface GenerationRequest {
   profile_id: string;
   text: string;
-  language: 'en' | 'zh';
+  language: LanguageCode;
   seed?: number;
   model_size?: '1.7B' | '0.6B';
 }
@@ -62,7 +63,7 @@ export interface HistoryListResponse {
 }
 
 export interface TranscriptionRequest {
-  language?: 'en' | 'zh';
+  language?: LanguageCode;
 }
 
 export interface TranscriptionResponse {

app/src/lib/hooks/useTranscription.ts

@@ -1,9 +1,10 @@
 import { useMutation } from '@tanstack/react-query';
 import { apiClient } from '@/lib/api/client';
+import type { LanguageCode } from '@/lib/constants/languages';
 
 export function useTranscription() {
   return useMutation({
-    mutationFn: ({ file, language }: { file: File; language?: 'en' | 'zh' }) =>
+    mutationFn: ({ file, language }: { file: File; language?: LanguageCode }) =>
       apiClient.transcribeAudio(file, language),
   });
 }