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.

auth/login.go

@@ -1,6 +1,7 @@
 package auth
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"log/slog"
@@ -14,13 +15,13 @@ import (
 
 var nameRegexp = regexp.MustCompile(`(\w+)同学`)
 
-// LoginWithClient 使用指定的 HTTP 客户端和凭据登录
-func LoginWithClient(httpClient *http.Client, captchaCode, username, password string) (bool, error) {
+// LoginWithClient 使用指定的 HTTP 客户端和凭据登录。
+func LoginWithClient(ctx context.Context, httpClient *http.Client, captchaCode, username, password string) (bool, error) {
 	log := slog.With("username", username)
 	log.Debug("执行登录")
 
 	data := fmt.Sprintf("usercode=%s&password=%s&code=%s", username, password, captchaCode)
-	req, err := http.NewRequest("POST", config.Get().BaseURL+"/login", strings.NewReader(data))
+	req, err := http.NewRequestWithContext(ctx, "POST", config.Get().BaseURL+"/login", strings.NewReader(data))
 	if err != nil {
 		return false, err
 	}
@@ -54,4 +55,4 @@ func LoginWithClient(httpClient *http.Client, captchaCode, username, password st
 		log.Warn("登录失败")
 	}
 	return false, nil
-}
+}