refactor(server): decouple services and improve architecture

- Introduce interfaces for all major services (JWT, PostAI, Comment, Message, Notification, QRCodeLogin, Upload, Vote, etc.) to support dependency inversion.
- Move query parameters from `internal/dto` to a new `internal/query` package to separate request payloads from data transfer objects.
- Refactor `internal/router` to use embedded `RouterDeps` for cleaner dependency management.
- Decouple handlers from repositories by injecting services instead of direct repository access, ensuring proper layering.
- Improve database initialization by moving it from `internal/model` to `internal/database`.
- Optimize message decryption by implementing a more efficient `BatchDecrypt` method in `MessageEncryptor` using a worker pool.
- Enhance error handling and security by implementing fail-fast checks for encryption key length during startup.
- Clean up unused code, including the `avatar` package and several unused DTOs.

internal/service/grade_sync_service.go

@@ -27,8 +27,15 @@ type SyncGradesResult struct {
 	ErrorMessage string `json:"error_message,omitempty"`
 }
 
+// GradeSummary 成绩查询结果（成绩列表 + GPA 概要）
+type GradeSummary struct {
+	Grades     []*model.Grade
+	GpaSummary *model.GpaSummary
+}
+
 type GradeSyncService interface {
 	SyncUserGrades(ctx context.Context, userID string, req *SyncGradesRequest) (*SyncGradesResult, error)
+	ListGradesWithSummary(userID string) (*GradeSummary, error)
 }
 
 type gradeSyncService struct {
@@ -158,4 +165,15 @@ func (s *gradeSyncService) saveGrades(ctx context.Context, userID string, grades
 		return fmt.Errorf("failed to create grades: %w", err)
 	}
 	return nil
-}
+}
+
+// ListGradesWithSummary 查询用户全部成绩及最新 GPA 概要。
+// GPA 概要查询失败不影响成绩返回（保持与历史 handler 行为一致）。
+func (s *gradeSyncService) ListGradesWithSummary(userID string) (*GradeSummary, error) {
+	grades, err := s.gradeRepo.ListByUser(userID)
+	if err != nil {
+		return nil, err
+	}
+	gpa, _ := s.gradeRepo.GetLatestGpaSummary(userID)
+	return &GradeSummary{Grades: grades, GpaSummary: gpa}, nil
+}