refactor: introduce service layer and migrate gRPC handlers to use it

Extract business logic from gRPC handlers into a dedicated service package.
Add context support throughout for cancellation and timeouts. Move models to
their own package, remove hardcoded credentials from config, and simplify
parsers to only handle HTML parsing.

grpc/handler_grades.go

@@ -7,8 +7,6 @@ import (
 
 	pb "schedule_converter/proto/runner"
 
-	"schedule_converter/config"
-	"schedule_converter/parser"
 	apperr "schedule_converter/pkg/errors"
 )
 
@@ -21,46 +19,11 @@ func (h *TaskHandler) getGrades(ctx context.Context, payload []byte) ([]byte, er
 	log := slog.With("username", req.Username, "semester", req.Semester)
 	log.Info("获取成绩任务")
 
-	httpClient, err := createHTTPClient()
+	result, err := h.service.GetGrades(ctx, &req)
 	if err != nil {
-		return nil, err
+		return nil, apperr.New("get_grades", err, "获取成绩失败")
 	}
 
-	cfg := config.Get()
-	setTWFIDCookie(httpClient, cfg.BaseURL, "")
-
-	if err := executeLogin(ctx, httpClient, req.Username, req.Password); err != nil {
-		return nil, err
-	}
-
-	var gpaSummary *pb.GpaSummary
-	summary, grades, err := parser.FetchGPA(httpClient)
-	if err != nil {
-		log.Warn("获取GPA页面失败，尝试成绩页面", "error", err)
-		grades, err = parser.FetchGrades(httpClient, parser.ScoreTypeFinal)
-		if err != nil {
-			return nil, apperr.New("fetch_grades", err, "获取成绩失败")
-		}
-	} else if summary != nil {
-		gpaSummary = &pb.GpaSummary{
-			AverageGpa:       summary.AverageGPA,
-			Rank:             summary.Rank,
-			ExamTotalGpa:     summary.ExamTotalGPA,
-			ExamTotalCredits: summary.ExamTotalCredits,
-			FailCredits:      summary.FailCredits,
-			Semesters:        summary.Semesters,
-		}
-	}
-
-	pbGrades := convertGrades(grades)
-
-	result := &pb.GradesResultData{
-		StudentId:  req.Username,
-		Semester:   req.Semester,
-		Grades:     pbGrades,
-		GpaSummary: gpaSummary,
-	}
-
-	log.Info("成绩获取成功", "grade_count", len(pbGrades))
+	log.Info("成绩获取成功", "grade_count", len(result.Grades))
 	return json.Marshal(result)
 }