feat: 录音浏览器端转16k单声道WAV，适配百度ASR

百度VOP只认pcm/wav/amr/m4a，浏览器录的webm/mp4不支持。
用Web Audio API在前端解码→混单声道→线性插值重采样16k→编码16bit PCM WAV，
零服务器依赖（不需ffmpeg）。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/pages/ai-chat/index.vue

@@ -117,12 +117,15 @@
 
     <!-- 输入区 -->
     <view class="input-bar">
-      <!-- 麦克风按钮 -->
+      <!-- 麦克风按钮（同时支持触摸和鼠标，方便桌面浏览器测试） -->
       <view
         :class="['mic-btn', recording ? 'recording' : '']"
         @touchstart.prevent="startRecord"
         @touchend.prevent="stopRecord"
         @touchcancel.prevent="cancelRecord"
+        @mousedown.prevent="startRecord"
+        @mouseup.prevent="stopRecord"
+        @mouseleave.prevent="onMicLeave"
       >
         <text class="mic-icon">{{ recording ? '●' : '🎤' }}</text>
       </view>
@@ -199,7 +202,15 @@ export default {
         this.mediaRecorder.start()
         this.recording = true
       } catch (err) {
-        uni.showToast({ title: '无法访问麦克风', icon: 'none' })
+        let msg = '无法访问麦克风'
+        if (!navigator.mediaDevices || !navigator.mediaDevices.getUserMedia) {
+          msg = '当前环境不支持录音（需HTTPS或localhost）'
+        } else if (err && err.name === 'NotAllowedError') {
+          msg = '麦克风权限被拒绝，请在浏览器允许'
+        } else if (err && err.name === 'NotFoundError') {
+          msg = '未检测到麦克风设备'
+        }
+        uni.showToast({ title: msg, icon: 'none', duration: 2500 })
       }
     },
 
@@ -216,30 +227,97 @@ export default {
       this.mediaRecorder.stop()
     },
 
+    // 鼠标移出按钮：录音中则发送（等同松手），未录音则忽略
+    onMicLeave(e) {
+      if (this.recording && this.mediaRecorder) {
+        this.recording = false
+        this.mediaRecorder.stop()
+      }
+    },
+
     async submitAudio() {
       const mimeType = (this.audioChunks[0] && this.audioChunks[0].type) || 'audio/webm'
-      const blob = new Blob(this.audioChunks, { type: mimeType })
-      const ext = mimeType.includes('mp4') ? 'm4a' : mimeType.includes('ogg') ? 'ogg' : 'webm'
-
-      const formData = new FormData()
-      formData.append('file', blob, 'voice.' + ext)
+      const srcBlob = new Blob(this.audioChunks, { type: mimeType })
 
       uni.showLoading({ title: '识别中...' })
       try {
+        // 浏览器端转成百度要求的 16k 单声道 16bit WAV
+        const wavBlob = await this.encodeWav16k(srcBlob)
+
+        const formData = new FormData()
+        formData.append('file', wavBlob, 'voice.wav')
+
         const resp = await fetch(ASR_URL, { method: 'POST', body: formData })
         const data = await resp.json()
         uni.hideLoading()
         if (data.success && data.text) {
           this.inputText = data.text
-          // 自动发送
           this.$nextTick(() => this.sendMessage())
         } else {
           uni.showToast({ title: data.message || '未识别到内容', icon: 'none' })
         }
       } catch (err) {
         uni.hideLoading()
-        uni.showToast({ title: '网络异常，请重试', icon: 'none' })
+        uni.showToast({ title: '识别失败：' + (err.message || '请重试'), icon: 'none' })
+      }
+    },
+
+    // 把任意录音 Blob 解码 → 混单声道 → 重采样16k → 编码16bit PCM WAV
+    async encodeWav16k(blob) {
+      const arrayBuffer = await blob.arrayBuffer()
+      const AudioCtx = window.AudioContext || window.webkitAudioContext
+      const ctx = new AudioCtx()
+      const decoded = await ctx.decodeAudioData(arrayBuffer)
+      ctx.close()
+
+      // 混成单声道
+      const numCh = decoded.numberOfChannels
+      const srcLen = decoded.length
+      const mono = new Float32Array(srcLen)
+      for (let ch = 0; ch < numCh; ch++) {
+        const ch_data = decoded.getChannelData(ch)
+        for (let i = 0; i < srcLen; i++) mono[i] += ch_data[i] / numCh
+      }
+
+      // 线性插值重采样到 16000
+      const dstRate = 16000
+      const srcRate = decoded.sampleRate
+      const dstLen = Math.round(srcLen * dstRate / srcRate)
+      const out = new Float32Array(dstLen)
+      const ratio = srcRate / dstRate
+      for (let i = 0; i < dstLen; i++) {
+        const pos = i * ratio
+        const idx = Math.floor(pos)
+        const frac = pos - idx
+        const s0 = mono[idx] || 0
+        const s1 = mono[idx + 1] || s0
+        out[i] = s0 + (s1 - s0) * frac
+      }
+
+      // 编码 WAV (44字节头 + 16bit PCM)
+      const buffer = new ArrayBuffer(44 + dstLen * 2)
+      const view = new DataView(buffer)
+      const writeStr = (off, str) => { for (let i = 0; i < str.length; i++) view.setUint8(off + i, str.charCodeAt(i)) }
+      writeStr(0, 'RIFF')
+      view.setUint32(4, 36 + dstLen * 2, true)
+      writeStr(8, 'WAVE')
+      writeStr(12, 'fmt ')
+      view.setUint32(16, 16, true)
+      view.setUint16(20, 1, true)        // PCM
+      view.setUint16(22, 1, true)        // 单声道
+      view.setUint32(24, dstRate, true)
+      view.setUint32(28, dstRate * 2, true)
+      view.setUint16(32, 2, true)
+      view.setUint16(34, 16, true)
+      writeStr(36, 'data')
+      view.setUint32(40, dstLen * 2, true)
+      let off = 44
+      for (let i = 0; i < dstLen; i++) {
+        let s = Math.max(-1, Math.min(1, out[i]))
+        view.setInt16(off, s < 0 ? s * 0x8000 : s * 0x7FFF, true)
+        off += 2
       }
+      return new Blob([view], { type: 'audio/wav' })
     },
 
     // ============ 导航 ============