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.

service/schedule.go

@@ -1,124 +0,0 @@
-package service
-
-import (
-	"context"
-	"log/slog"
-	"net/http"
-	"time"
-
-	"schedule_converter/auth"
-	"schedule_converter/captcha"
-	"schedule_converter/client"
-	"schedule_converter/config"
-	"schedule_converter/models"
-	"schedule_converter/parser"
-	apperr "schedule_converter/pkg/errors"
-)
-
-type ScheduleService struct {
-	httpClient *http.Client
-	maxRetries int
-	retryDelay time.Duration
-}
-
-type ScheduleOption func(*ScheduleService)
-
-func WithMaxRetries(n int) ScheduleOption {
-	return func(s *ScheduleService) {
-		s.maxRetries = n
-	}
-}
-
-func WithRetryDelay(d time.Duration) ScheduleOption {
-	return func(s *ScheduleService) {
-		s.retryDelay = d
-	}
-}
-
-func NewScheduleService(opts ...ScheduleOption) *ScheduleService {
-	s := &ScheduleService{
-		httpClient: client.Client,
-		maxRetries: 3,
-		retryDelay: 3 * time.Second,
-	}
-	for _, opt := range opts {
-		opt(s)
-	}
-	return s
-}
-
-func NewScheduleServiceWithClient(httpClient *http.Client, opts ...ScheduleOption) *ScheduleService {
-	s := &ScheduleService{
-		httpClient: httpClient,
-		maxRetries: 3,
-		retryDelay: 3 * time.Second,
-	}
-	for _, opt := range opts {
-		opt(s)
-	}
-	return s
-}
-
-func (s *ScheduleService) FetchSchedule(ctx context.Context, username, password, semester string) ([]models.Course, error) {
-	log := slog.With("username", username, "semester", semester)
-
-	if err := client.GetInitialCookiesWithClient(s.httpClient); err != nil {
-		return nil, apperr.New("fetch_schedule", err, "获取Cookie失败")
-	}
-
-	var lastErr error
-	for attempt := 1; attempt <= s.maxRetries; attempt++ {
-		select {
-		case <-ctx.Done():
-			return nil, ctx.Err()
-		default:
-		}
-
-		log.Info("尝试登录", "attempt", attempt, "max_retries", s.maxRetries)
-
-		captchaCode, err := captcha.GetAndRecognize(s.httpClient)
-		if err != nil {
-			log.Warn("验证码获取失败", "error", err, "attempt", attempt)
-			lastErr = err
-			time.Sleep(s.retryDelay)
-			continue
-		}
-
-		success, err := auth.LoginWithClient(s.httpClient, captchaCode, username, password)
-		if err != nil {
-			log.Warn("登录失败", "error", err, "attempt", attempt)
-			lastErr = err
-			time.Sleep(s.retryDelay)
-			continue
-		}
-
-		if success {
-			if semester == "" {
-				semester = config.Semester
-			}
-			courses, err := parser.FetchScheduleWithClient(s.httpClient, semester)
-			if err != nil {
-				return nil, apperr.New("fetch_schedule", err, "获取课表失败")
-			}
-			log.Info("获取课表成功", "course_count", len(courses))
-			return courses, nil
-		}
-
-		log.Warn("登录验证失败，稍后重试", "attempt", attempt)
-		time.Sleep(s.retryDelay)
-	}
-
-	return nil, apperr.New("fetch_schedule", lastErr, "登录失败，已重试")
-}
-
-func (s *ScheduleService) FetchDefaultSchedule(ctx context.Context) ([]models.Course, error) {
-	return s.FetchSchedule(ctx, config.Username, config.Password, config.Semester)
-}
-
-func (s *ScheduleService) FetchScheduleForUser(username, password, semester string) ([]models.Course, error) {
-	return s.FetchSchedule(context.Background(), username, password, semester)
-}
-
-func (s *ScheduleService) FetchDefaultScheduleLegacy() ([]models.Course, error) {
-	return s.FetchScheduleForUser(config.Username, config.Password, config.Semester)
-}