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.

pkg/errors/errors.go

@@ -7,25 +7,26 @@ import (
 
 var ErrLoginFailed = errors.New("login failed")
 
-type ScheduleError struct {
+// AppError 携带操作名（Op）与中文提示（Msg）的错误类型，用于统一日志与错误上报。
+type AppError struct {
 	Op  string
 	Err error
 	Msg string
 }
 
-func (e *ScheduleError) Error() string {
+func (e *AppError) Error() string {
 	if e.Msg != "" {
 		return fmt.Sprintf("%s: %s: %v", e.Op, e.Msg, e.Err)
 	}
 	return fmt.Sprintf("%s: %v", e.Op, e.Err)
 }
 
-func (e *ScheduleError) Unwrap() error {
+func (e *AppError) Unwrap() error {
 	return e.Err
 }
 
 func New(op string, err error, msg string) error {
-	return &ScheduleError{
+	return &AppError{
 		Op:  op,
 		Err: err,
 		Msg: msg,