feat: enhance completion service with session management and language support

- Introduced session management using Redis for tracking active sessions.
- Added session claiming and releasing functionality in the completion manager.
- Enhanced HTTP and WebSocket completion endpoints to support multiple languages.
- Implemented request timeout and maximum body size configurations for API routes.
- Updated client-side code to handle session IDs and language parameters in completion requests.
- Improved error handling for unsupported languages and session conflicts.
- Added tests for the completion manager to ensure proper session handling and cleanup.

backend/internal/completion/service.go

@@ -10,6 +10,8 @@ import (
 var ErrInvalidRequest = errors.New("invalid completion request")
 
 type Request struct {
+	Language  string `json:"language,omitempty"`
+	SessionID string `json:"sessionId,omitempty"`
 	URI       string `json:"uri"`
 	Text      string `json:"text"`
 	Line      int    `json:"line"`