feat(call): implement group calling and enhance call management

Introduces group calling capabilities, including group invites and participant
lifecycle management. Enhances the existing call system with support for
media types (voice/video) and improved participant tracking.

- Add `GroupInvite` and `ParticipantJoin/Leave` to `CallService`.
- Implement WebSocket handlers for `call_group_invite` and
  `call_participant_join`.
- Update `CallSession` model to support group IDs, media types, and
  tracking who ended the call.
- Integrate `GroupService` into `CallService` via dependency injection.
- Add error constants for group call limitations and participant capacity.
- Update LiveKit webhook handling to process participant leave events.

Refactor grade synchronization to remove semester-based filtering in favor
of a more flexible user-based approach and improve GPA summary updates.

internal/service/livekit_service.go

@@ -17,9 +17,15 @@ import (
 	"google.golang.org/protobuf/encoding/protojson"
 )
 
+// RoomConfig 房间配置选项
+type RoomConfig struct {
+	MaxParticipants uint32
+	EmptyTimeout    uint32 // 秒
+}
+
 // LiveKitService LiveKit 令牌生成和 Webhook 处理服务
 type LiveKitService interface {
-	GenerateToken(roomName, userID string, canPublish, canSubscribe bool) (string, error)
+	GenerateToken(roomName, userID string, canPublish, canSubscribe bool, roomCfg ...RoomConfig) (string, error)
 	ProcessWebhook(ctx context.Context, body []byte, authHeader string) (*livekit.WebhookEvent, error)
 }
 
@@ -37,7 +43,7 @@ func NewLiveKitService(cfg *config.Config, logger *zap.Logger) LiveKitService {
 }
 
 // GenerateToken 为指定 room 和 user 生成 LiveKit 访问令牌
-func (s *liveKitService) GenerateToken(roomName, userID string, canPublish, canSubscribe bool) (string, error) {
+func (s *liveKitService) GenerateToken(roomName, userID string, canPublish, canSubscribe bool, roomCfg ...RoomConfig) (string, error) {
 	if !s.config.Enabled {
 		return "", fmt.Errorf("livekit is not enabled")
 	}
@@ -57,8 +63,9 @@ func (s *liveKitService) GenerateToken(roomName, userID string, canPublish, canS
 		Room:           roomName,
 		CanPublish:     &canPublish,
 		CanSubscribe:   &canSubscribe,
-		CanPublishData: &canSubscribe,
+		CanPublishData: &canPublish,
 	}
+
 	at.SetVideoGrant(grant)
 
 	token, err := at.ToJWT()