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.

parser/schedule.go

@@ -1,16 +1,11 @@
 package parser
 
 import (
-	"fmt"
-	"io"
-	"net/http"
 	"regexp"
 	"sort"
 	"strconv"
 	"strings"
 
-	"schedule_converter/client"
-	"schedule_converter/config"
 	"schedule_converter/models"
 
 	"github.com/PuerkitoBio/goquery"
@@ -23,32 +18,6 @@ type weekRoomEntry struct {
 	room     string
 }
 
-// 获取课表
-// FetchScheduleWithClient 使用指定的 HTTP 客户端和学期获取课表
-func FetchScheduleWithClient(httpClient *http.Client, semester string) ([]models.Course, error) {
-	// POST请求获取课表
-	data := fmt.Sprintf("xnxq=%s", semester)
-	req, err := http.NewRequest("POST", config.Get().BaseURL+"/kbcx/queryGrkb", strings.NewReader(data))
-	if err != nil {
-		return nil, err
-	}
-
-	req.Header = client.GetHeadersWithContentType("application/x-www-form-urlencoded")
-
-	resp, err := httpClient.Do(req)
-	if err != nil {
-		return nil, err
-	}
-	defer resp.Body.Close()
-
-	body, err := io.ReadAll(resp.Body)
-	if err != nil {
-		return nil, err
-	}
-
-	return ParseScheduleHTML(string(body))
-}
-
 // 解析课表HTML
 func ParseScheduleHTML(html string) ([]models.Course, error) {
 	// 创建一个带Reader的Document