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/handler/exam_handler.go

@@ -4,19 +4,16 @@ import (
 	"github.com/gin-gonic/gin"
 
 	"with_you/internal/pkg/response"
-	"with_you/internal/repository"
 	"with_you/internal/service"
 )
 
 type ExamHandler struct {
 	examSyncService service.ExamSyncService
-	examRepo        repository.ExamRepository
 }
 
-func NewExamHandler(examSyncService service.ExamSyncService, examRepo repository.ExamRepository) *ExamHandler {
+func NewExamHandler(examSyncService service.ExamSyncService) *ExamHandler {
 	return &ExamHandler{
 		examSyncService: examSyncService,
-		examRepo:        examRepo,
 	}
 }
 
@@ -68,7 +65,7 @@ func (h *ExamHandler) ListExams(c *gin.Context) {
 		return
 	}
 
-	exams, err := h.examRepo.ListByUserAndSemester(userID, semester)
+	exams, err := h.examSyncService.ListExams(userID, semester)
 	if err != nil {
 		response.HandleError(c, err, "failed to list exams")
 		return