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_exams.go

@@ -7,8 +7,6 @@ import (
 
 	pb "schedule_converter/proto/runner"
 
-	"schedule_converter/config"
-	"schedule_converter/parser"
 	apperr "schedule_converter/pkg/errors"
 )
 
@@ -21,31 +19,11 @@ func (h *TaskHandler) getExams(ctx context.Context, payload []byte) ([]byte, err
 	log := slog.With("username", req.Username, "semester", req.Semester)
 	log.Info("获取考试安排任务")
 
-	httpClient, err := createHTTPClient()
+	result, err := h.service.GetExams(ctx, &req)
 	if err != nil {
-		return nil, err
+		return nil, apperr.New("get_exams", err, "获取考试安排失败")
 	}
 
-	cfg := config.Get()
-	setTWFIDCookie(httpClient, cfg.BaseURL, "")
-
-	if err := executeLogin(ctx, httpClient, req.Username, req.Password); err != nil {
-		return nil, err
-	}
-
-	exams, err := parser.FetchAllExams(httpClient)
-	if err != nil {
-		return nil, apperr.New("fetch_exams", err, "获取考试安排失败")
-	}
-
-	pbExams := convertExams(exams)
-
-	result := &pb.ExamsResultData{
-		StudentId: req.Username,
-		Semester:  req.Semester,
-		Exams:     pbExams,
-	}
-
-	log.Info("考试安排获取成功", "exam_count", len(pbExams))
+	log.Info("考试安排获取成功", "exam_count", len(result.Exams))
 	return json.Marshal(result)
 }