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/exam_sync_service.go

@@ -29,12 +29,13 @@ type SyncExamsResult struct {
 
 type ExamSyncService interface {
 	SyncUserExams(ctx context.Context, userID string, req *SyncExamsRequest) (*SyncExamsResult, error)
+	ListExams(userID, semester string) ([]*model.Exam, error)
 }
 
 type examSyncService struct {
 	taskManager *runner.TaskManager
-	examRepo   repository.ExamRepository
-	logger     *zap.Logger
+	examRepo    repository.ExamRepository
+	logger      *zap.Logger
 }
 
 func NewExamSyncService(
@@ -128,4 +129,9 @@ func (s *examSyncService) saveExams(ctx context.Context, userID, semester string
 		return fmt.Errorf("failed to create exams: %w", err)
 	}
 	return nil
-}
+}
+
+// ListExams 查询用户某学期的考试安排。
+func (s *examSyncService) ListExams(userID, semester string) ([]*model.Exam, error) {
+	return s.examRepo.ListByUserAndSemester(userID, semester)
+}