feat(backend): Go 服务骨架（配置、日志、数据库、中间件、Wire）

- config: Viper YAML 配置 + 环境变量覆盖
- logs: zap 结构化日志 + trace_id 链路追踪 + 敏感信息脱敏
- db: PostgreSQL (GORM) + Redis (go-redis) 连接管理
- middleware: Trace/Logger/CORS/Recovery 四层中间件
- provider: Wire 编译时依赖注入
- main.go: 优雅启动/关闭 HTTP 服务

Made-with: Cursor

backend/go-service/pkg/middleware/recovery.go

@@ -0,0 +1,36 @@
+package middleware
+
+import (
+	"net/http"
+	"runtime/debug"
+
+	"github.com/echochat/backend/pkg/logs"
+	"github.com/echochat/backend/pkg/utils"
+	"github.com/gin-gonic/gin"
+	"go.uber.org/zap"
+)
+
+// Recovery Panic 恢复中间件
+// 捕获 panic 后记录 ERROR 日志含堆栈信息，返回 500 响应
+func Recovery() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		defer func() {
+			if r := recover(); r != nil {
+				ctx := c.Request.Context()
+				logs.Error(ctx, "middleware.Recovery", "服务发生 panic",
+					zap.Any("error", r),
+					zap.String("stack", string(debug.Stack())),
+					zap.String("path", c.Request.URL.Path),
+					zap.String("method", c.Request.Method),
+				)
+
+				c.AbortWithStatusJSON(http.StatusInternalServerError, utils.Response{
+					Code:    500,
+					Message: "服务内部错误",
+					TraceID: logs.GetTraceID(ctx),
+				})
+			}
+		}()
+		c.Next()
+	}
+}