feat: 实现 Gin trace 中间件生成并注入 trace ID

backend/internal/trace/middleware.go

@@ -0,0 +1,17 @@
+package trace
+
+import "github.com/gin-gonic/gin"
+
+// TraceMiddleware 为每个 HTTP 请求生成 trace ID 并注入 context
+func TraceMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		traceID := GenerateTraceID()
+		ctx := WithTraceID(c.Request.Context(), traceID)
+		ctx = WithRequestID(ctx, traceID) // REST: trace_id == request_id
+
+		c.Request = c.Request.WithContext(ctx)
+		c.Header("X-Trace-ID", traceID) // 返回给客户端用于排查
+
+		c.Next()
+	}
+}