refactor(grpc): restructure task handling and migrate to slog

Refactor the gRPC client and task handling logic to improve modularity,
error handling, and observability.

- Split `grpc/handler.go` into specialized handler files (login,
  classroom, exams, grades, schedule) to reduce complexity.
- Replace standard `log` with `log/slog` throughout the project for
  structured logging.
- Refactor `grpc/client.go` to use a thread-safe connection management
  pattern with `sync.RWMutex`.
- Remove the legacy `service` package and HTTP server implementation,
  transitioning the application to a pure gRPC runner mode.
- Clean up `config` and `pkg/errors` to remove unused utilities and
  simplify the API.
- Improve error reporting in parsers and HTTP clients by checking
  response status codes.

parser/exam.go

@@ -2,6 +2,7 @@ package parser
 
 import (
 	"fmt"
+	"log/slog"
 	"net/http"
 	"strings"
 
@@ -40,8 +41,9 @@ func examTypeToCode(t ExamType) string {
 }
 
 func FetchExams(httpClient *http.Client, examType ExamType) ([]ExamEntry, error) {
-	examURL := config.BaseURL + "/kscx/queryKsForXs"
-	fmt.Printf("[考试] 正在获取考试时间数据 (%s)...\n", examType)
+	examURL := config.Get().BaseURL + "/kscx/queryKsForXs"
+	log := slog.With("exam_type", string(examType))
+	log.Info("获取考试时间数据")
 
 	data := fmt.Sprintf("xnxq=&kssjd=%s", examTypeToCode(examType))
 	req, err := http.NewRequest("POST", examURL, strings.NewReader(data))
@@ -57,34 +59,43 @@ func FetchExams(httpClient *http.Client, examType ExamType) ([]ExamEntry, error)
 	}
 	defer resp.Body.Close()
 
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("获取考试数据失败, 状态码: %d", resp.StatusCode)
+	}
+
 	html, err := decodeResponseBody(resp)
 	if err != nil {
 		return nil, err
 	}
 
-	exams, err := ParseExamTimeHTML(html, examType)
+	exams, err := parseExamTimeHTML(html, examType)
 	if err != nil {
 		return nil, err
 	}
 
-	fmt.Printf("[考试] 共获取 %d 条考试记录 (%s)\n", len(exams), examType)
+	log.Info("考试数据获取完成", "exam_count", len(exams))
 	return exams, nil
 }
 
 func FetchAllExams(httpClient *http.Client) ([]ExamEntry, error) {
 	var allExams []ExamEntry
+	var lastErr error
 	for _, et := range []ExamType{ExamTypeFinal, ExamTypeMidterm, ExamTypeMakeup} {
 		exams, err := FetchExams(httpClient, et)
 		if err != nil {
-			fmt.Printf("[考试] 获取%s考试失败: %v\n", et, err)
+			slog.Warn("获取考试数据失败", "exam_type", string(et), "error", err)
+			lastErr = err
 			continue
 		}
 		allExams = append(allExams, exams...)
 	}
+	if len(allExams) == 0 && lastErr != nil {
+		return nil, fmt.Errorf("所有考试类型获取均失败: %w", lastErr)
+	}
 	return allExams, nil
 }
 
-func ParseExamTimeHTML(html string, examType ExamType) ([]ExamEntry, error) {
+func parseExamTimeHTML(html string, examType ExamType) ([]ExamEntry, error) {
 	doc, err := goquery.NewDocumentFromReader(strings.NewReader(html))
 	if err != nil {
 		return nil, err