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.

service/exams.go

@@ -0,0 +1,79 @@
+package service
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"strings"
+
+	"schedule_converter/client"
+	"schedule_converter/models"
+	"schedule_converter/parser"
+	apperr "schedule_converter/pkg/errors"
+
+	pb "schedule_converter/proto/runner"
+)
+
+var allExamTypes = []models.ExamType{models.ExamTypeFinal, models.ExamTypeMidterm, models.ExamTypeMakeup}
+
+// GetExams 获取考试安排：登录 → 遍历各考试类型抓取并解析 → 合并 → 转换为 pb 结果。
+func (s *Service) GetExams(ctx context.Context, req *pb.GetExamsPayload) (*pb.ExamsResultData, error) {
+	log := slog.With("username", req.Username, "semester", req.Semester)
+
+	httpClient, err := s.newAuthenticatedClient(ctx, req.Username, req.Password, "")
+	if err != nil {
+		return nil, err
+	}
+
+	var allExams []models.ExamEntry
+	var lastErr error
+	for _, et := range allExamTypes {
+		data := fmt.Sprintf("xnxq=&kssjd=%s", parser.ExamTypeCode(et))
+		html, ferr := client.FetchHTML(ctx, httpClient, "POST", "/kscx/queryKsForXs", strings.NewReader(data), "application/x-www-form-urlencoded", "")
+		if ferr != nil {
+			log.Warn("获取考试数据失败", "exam_type", string(et), "error", ferr)
+			lastErr = ferr
+			continue
+		}
+		exams, perr := parser.ParseExamHTML(html, et)
+		if perr != nil {
+			log.Warn("解析考试数据失败", "exam_type", string(et), "error", perr)
+			lastErr = perr
+			continue
+		}
+		allExams = append(allExams, exams...)
+	}
+
+	if len(allExams) == 0 && lastErr != nil {
+		return nil, apperr.New("fetch_exams", lastErr, "所有考试类型获取均失败")
+	}
+
+	return &pb.ExamsResultData{
+		StudentId: req.Username,
+		Semester:  req.Semester,
+		Exams:     convertExams(allExams),
+	}, nil
+}
+
+// convertExams 将内部考试模型转换为 pb.Exam 列表。
+func convertExams(exams []models.ExamEntry) []*pb.Exam {
+	result := make([]*pb.Exam, 0, len(exams))
+	for _, e := range exams {
+		examTypeStr := "期末"
+		switch e.Type {
+		case models.ExamTypeMidterm:
+			examTypeStr = "期中"
+		case models.ExamTypeMakeup:
+			examTypeStr = "补考"
+		}
+		result = append(result, &pb.Exam{
+			CourseName: e.Course,
+			ExamType:   examTypeStr,
+			Date:       e.Date,
+			Time:       e.Time,
+			Week:       e.Week,
+			Weekday:    e.Weekday,
+		})
+	}
+	return result
+}