feat: 新增语音转文字（ASR）功能

- 后端：新增 /api/audio/transcribe 接口，调用 Ollama whisper 进行语音识别
- 前端：新增 AudioTranscribePage.vue 页面，支持 MP3/WAV/M4A/OGG/FLAC 等格式
- 注册路由、工具卡片、智能助手欢迎语更新

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

eai_agentplatform/backend-go/internal/web/response.go

@@ -0,0 +1,17 @@
+package web
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+// OK 成功响应信封 {"data": ..., "error": null, "message": "success"}
+func OK(c *gin.Context, data any) {
+	c.JSON(http.StatusOK, gin.H{"data": data, "error": nil, "message": "success"})
+}
+
+// Fail 错误响应信封 {"data": null, "error": ..., "message": ...}
+func Fail(c *gin.Context, e *AppError) {
+	c.JSON(e.StatusCode, gin.H{"data": nil, "error": e.Code, "message": e.Message})
+}