feat: enhance API and session management with Nacos and Redis integration

- Add Nacos registry for service registration and deregistration.
- Implement Redis registry for session management with heartbeat and session claiming.
- Improve completion service with session handling and request validation.
- Enhance WebSocket handling for completion requests with JSON-RPC support.
- Add tests for new registry implementations and completion manager functionalities.
- Refactor existing code for better readability and maintainability.

backend/internal/api/handler.go

@@ -15,15 +15,18 @@ type CompletionService interface {
 	Complete(ctx context.Context, req completion.Request) (completion.Response, error)
 }
 
+// SessionStatsProvider 暴露会话统计信息，供就绪探针输出。
 type SessionStatsProvider interface {
 	ActiveSessions() map[string]int
 }
 
+// RouteOptions 控制 HTTP/WS 接口的超时与请求体上限。
 type RouteOptions struct {
-	RequestTimeout time.Duration
-	MaxBodyBytes   int64
+	RequestTimeout time.Duration // 单次补全调用超时时间。
+	MaxBodyBytes   int64         // 请求体最大字节数（HTTP/WS 共用）。
 }
 
+// RegisterRoutes 注册健康检查、HTTP 补全接口和 WebSocket 补全接口。
 func RegisterRoutes(router *gin.Engine, service CompletionService, options ...RouteOptions) {
 	opts := RouteOptions{
 		RequestTimeout: 10 * time.Second,
@@ -60,6 +63,7 @@ func RegisterRoutes(router *gin.Engine, service CompletionService, options ...Ro
 	registerWSRoutes(router, service, opts)
 
 	handleCompletion := func(c *gin.Context) {
+		// 为单次请求限制 body 大小，避免异常大包占满内存。
 		c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, opts.MaxBodyBytes)
 		var req completion.Request
 		if err := c.ShouldBindJSON(&req); err != nil {
@@ -68,10 +72,12 @@ func RegisterRoutes(router *gin.Engine, service CompletionService, options ...Ro
 		}
 
 		routeLang := c.Param("language")
+		// 若 body 未显式给出 language，则使用路由参数。
 		if req.Language == "" {
 			req.Language = routeLang
 		}
 
+		// 对下游补全调用增加超时保护，防止请求长时间悬挂。
 		ctx, cancel := context.WithTimeout(c.Request.Context(), opts.RequestTimeout)
 		defer cancel()