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/grade_sync_service.go

@@ -81,7 +81,7 @@ func (s *gradeSyncService) SyncUserGrades(ctx context.Context, userID string, re
 	}
 
 	grades := s.convertGrades(userID, &resultData)
-	if err := s.saveGrades(ctx, userID, resultData.Semester, grades); err != nil {
+	if err := s.saveGrades(ctx, userID, grades); err != nil {
 		s.logger.Error("failed to save grades",
 			zap.String("user_id", userID),
 			zap.Error(err))
@@ -89,7 +89,12 @@ func (s *gradeSyncService) SyncUserGrades(ctx context.Context, userID string, re
 	}
 
 	if resultData.GpaSummary != nil {
-		summary := s.convertGpaSummary(userID, resultData.Semester, resultData.GpaSummary)
+		if err := s.gradeRepo.DeleteGpaSummaryByUser(ctx, userID); err != nil {
+			s.logger.Warn("failed to delete old gpa summary",
+				zap.String("user_id", userID),
+				zap.Error(err))
+		}
+		summary := s.convertGpaSummary(userID, resultData.GpaSummary)
 		if err := s.gradeRepo.SaveGpaSummary(ctx, summary); err != nil {
 			s.logger.Warn("failed to save gpa summary",
 				zap.String("user_id", userID),
@@ -128,11 +133,11 @@ func (s *gradeSyncService) convertGrades(userID string, data *pb.GradesResultDat
 	return grades
 }
 
-func (s *gradeSyncService) convertGpaSummary(userID, semester string, gpa *pb.GpaSummary) *model.GpaSummary {
+func (s *gradeSyncService) convertGpaSummary(userID string, gpa *pb.GpaSummary) *model.GpaSummary {
 	return &model.GpaSummary{
 		ID:               uuid.New().String(),
 		UserID:           userID,
-		Semester:         semester,
+		Semester:         gpa.Semesters,
 		AverageGpa:       gpa.AverageGpa,
 		Rank:             gpa.Rank,
 		ExamTotalGpa:     gpa.ExamTotalGpa,
@@ -142,8 +147,8 @@ func (s *gradeSyncService) convertGpaSummary(userID, semester string, gpa *pb.Gp
 	}
 }
 
-func (s *gradeSyncService) saveGrades(ctx context.Context, userID, semester string, grades []*model.Grade) error {
-	if err := s.gradeRepo.DeleteByUserAndSemester(ctx, userID, semester); err != nil {
+func (s *gradeSyncService) saveGrades(ctx context.Context, userID string, grades []*model.Grade) error {
+	if err := s.gradeRepo.DeleteByUser(ctx, userID); err != nil {
 		return fmt.Errorf("failed to delete old grades: %w", err)
 	}
 	if len(grades) == 0 {