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_login.go

@@ -7,7 +7,7 @@ import (
 
 	pb "schedule_converter/proto/runner"
 
-	"schedule_converter/config"
+	apperr "schedule_converter/pkg/errors"
 )
 
 func (h *TaskHandler) login(ctx context.Context, payload []byte) ([]byte, error) {
@@ -19,16 +19,8 @@ func (h *TaskHandler) login(ctx context.Context, payload []byte) ([]byte, error)
 	log := slog.With("username", req.Username)
 	log.Info("登录任务")
 
-	httpClient, err := createHTTPClient()
-	if err != nil {
-		return nil, err
-	}
-
-	cfg := config.Get()
-	setTWFIDCookie(httpClient, cfg.BaseURL, req.Twfid)
-
-	if err := executeLogin(ctx, httpClient, req.Username, req.Password); err != nil {
-		return nil, err
+	if _, err := h.service.Login(ctx, req.Username, req.Password, req.Twfid); err != nil {
+		return nil, apperr.New("login", err, "登录失败")
 	}
 
 	log.Info("登录成功")