feat(server): add request ID middleware

Add request ID middleware to trace requests through the system. The middleware checks for existing X-Request-ID headers, generates a new UUID if not present, and sets the ID in both request/response headers and Gin context.

internal/middleware/request_id.go

@@ -0,0 +1,35 @@
+package middleware
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"strings"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+// RequestID ensures every request has an X-Request-ID and echoes it back to the client.
+func RequestID() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		id := strings.TrimSpace(c.GetHeader("X-Request-ID"))
+		if id == "" {
+			id = strings.TrimSpace(c.GetHeader("X-Request-Id"))
+		}
+		if id == "" {
+			id = newRequestID()
+		}
+		c.Request.Header.Set("X-Request-ID", id)
+		c.Writer.Header().Set("X-Request-ID", id)
+		c.Set("request_id", id)
+		c.Next()
+	}
+}
+
+func newRequestID() string {
+	var b [16]byte
+	if _, err := rand.Read(b[:]); err != nil {
+		return hex.EncodeToString([]byte(time.Now().Format(time.RFC3339Nano)))
+	}
+	return hex.EncodeToString(b[:])
+}