feat: Implement Aliyun TTS backend integration and API key management

qwen3-tts-frontend/src/components/tts/VoiceCloneForm.tsx

@@ -37,6 +37,7 @@ const formSchema = z.object({
   top_k: z.number().min(1).max(100).optional(),
   top_p: z.number().min(0).max(1).optional(),
   repetition_penalty: z.number().min(0).max(2).optional(),
+  backend: z.string().optional(),
 })
 
 type FormData = z.infer<typeof formSchema>
@@ -75,6 +76,7 @@ function VoiceCloneForm() {
       top_k: 20,
       top_p: 0.7,
       repetition_penalty: 1.05,
+      backend: 'local',
     } as Partial<FormData>,
   })
 
@@ -233,6 +235,22 @@ function VoiceCloneForm() {
 
       <div className={step === 2 ? 'block space-y-4' : 'hidden'}>
         {/* Step 2: Synthesis Options */}
+        <div className="space-y-0.5">
+          <Label>后端选择</Label>
+          <Select
+            value={watch('backend')}
+            onValueChange={(value: string) => setValue('backend', value)}
+          >
+            <SelectTrigger>
+              <SelectValue />
+            </SelectTrigger>
+            <SelectContent>
+              <SelectItem value="local">本地模型</SelectItem>
+              <SelectItem value="aliyun">阿里云 API</SelectItem>
+            </SelectContent>
+          </Select>
+        </div>
+
         <div className="space-y-0.5">
           <IconLabel icon={Globe2} tooltip="语言（可选）" />
           <Select