fix: 录音可靠性修复 + ASR 后端优化

前端:
- recorder.onError 时重置 recorder = null，避免错误后录音永久失效
- 增加 asrLoading 状态，ASR 处理中输入框 disabled 并显示'语音识别中...'
- 增加 skipAsr 标志，<1s 的录音跳过 ASR 上传
- uploadFile 增加 30s timeout

后端:
- ASR: OpenAI 失败后 fallback 到本地 whisper，日志级别降为 warn
- try/catch/finally 重构，确保临时文件在所有路径都清理
- OpenAI 和 whisper 结果分别 try，互不影响

backend/src/modules/tts/tts.controller.ts

@@ -69,29 +69,38 @@ export class TtsController {
     }
 
     try {
+      let text = ''
       if (process.env.OPENAI_API_KEY) {
-        const result = execSync(
-          `curl -s -X POST https://api.openai.com/v1/audio/transcriptions \
-            -H "Authorization: Bearer ${process.env.OPENAI_API_KEY}" \
-            -H "Content-Type: multipart/form-data" \
-            -F "file=@${wavPath}" \
-            -F "model=whisper-1" \
-            -F "language=zh"`,
-          { encoding: 'utf8', timeout: 30000 },
+        try {
+          const result = execSync(
+            `curl -s -X POST https://api.openai.com/v1/audio/transcriptions \
+              -H "Authorization: Bearer ${process.env.OPENAI_API_KEY}" \
+              -H "Content-Type: multipart/form-data" \
+              -F "file=@${wavPath}" \
+              -F "model=whisper-1" \
+              -F "language=zh"`,
+            { encoding: 'utf8', timeout: 30000 },
+          )
+          const parsed = JSON.parse(result)
+          if (parsed.text) text = parsed.text.trim()
+        } catch (e: any) {
+          this.logger.warn(`OpenAI ASR failed, falling back to local: ${e.message}`)
+        }
+      }
+      if (!text) {
+        const whisperResult = execSync(
+          `python3 -c 'import sys, whisper; model = whisper.load_model("tiny"); print(model.transcribe(sys.argv[1], language="zh")["text"].strip())' "${wavPath}"`,
+          { encoding: 'utf8', timeout: 60000 },
         )
-        const parsed = JSON.parse(result)
-        if (parsed.text) return { text: parsed.text.trim() }
-      }
-      const whisperResult = execSync(`python3 -c 'import sys, whisper; model = whisper.load_model("tiny"); print(model.transcribe(sys.argv[1], language="zh")["text"].strip())' "${wavPath}"`, { encoding: 'utf8', timeout: 60000 })
-      if (whisperResult && whisperResult.trim()) {
-        return { text: whisperResult.trim() }
+        if (whisperResult?.trim()) text = whisperResult.trim()
       }
+      return { text }
     } catch (e: any) {
       this.logger.error(`ASR failed: ${e?.message || e}`)
+      return { text: '' }
+    } finally {
+      try { if (dest) fs.unlinkSync(dest) } catch {}
+      try { if (wavPath && wavPath !== dest) fs.unlinkSync(wavPath) } catch {}
     }
-    // 清理临时文件
-    try { if (dest) fs.unlinkSync(dest) } catch {}
-    try { if (wavPath && wavPath !== dest) fs.unlinkSync(wavPath) } catch {}
-    return { text: '' }
   }
 }