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/completion/service.go

@@ -9,6 +9,7 @@ import (
 
 var ErrInvalidRequest = errors.New("invalid completion request")
 
+// Request 是统一的补全请求模型。
 type Request struct {
 	Language  string `json:"language,omitempty"`
 	SessionID string `json:"sessionId,omitempty"`
@@ -18,6 +19,7 @@ type Request struct {
 	Character int    `json:"character"`
 }
 
+// Item 对应一个补全候选项。
 type Item struct {
 	Label         string `json:"label"`
 	Kind          int    `json:"kind,omitempty"`
@@ -28,11 +30,13 @@ type Item struct {
 	FilterText    string `json:"filterText,omitempty"`
 }
 
+// Response 是补全结果集合。
 type Response struct {
 	Items        []Item `json:"items"`
 	IsIncomplete bool   `json:"isIncomplete"`
 }
 
+// Client 抽象 LSP 客户端所需的最小能力。
 type Client interface {
 	DidOpen(ctx context.Context, uri, text string, version int) error
 	DidChange(ctx context.Context, uri, text string, version int) error
@@ -43,6 +47,7 @@ type documentState struct {
 	version int
 }
 
+// Service 负责文档生命周期同步（didOpen/didChange）与补全调用。
 type Service struct {
 	client Client
 
@@ -57,6 +62,7 @@ func NewService(client Client) *Service {
 	}
 }
 
+// Complete 根据 URI 的历史状态决定发送 didOpen 或 didChange，再请求补全。
 func (s *Service) Complete(ctx context.Context, req Request) (Response, error) {
 	if err := validateRequest(req); err != nil {
 		return Response{}, err
@@ -86,6 +92,7 @@ func (s *Service) Complete(ctx context.Context, req Request) (Response, error) {
 	return resp, nil
 }
 
+// validateRequest 做基础参数校验，避免向 LSP 发送非法请求。
 func validateRequest(req Request) error {
 	if req.URI == "" {
 		return ErrInvalidRequest