feat(admin): 添加提示词批量删除和定时同步功能

- 后端新增批量删除提示词接口和实现
- 前端管理页面添加多选和批量删除功能
- 添加定时同步GitHub远程提示词源功能
- 新增系统设置中的提示词同步配置选项
- 更新文档说明新的批量操作和定时同步功能
- 添加相关的测试用例和依赖库

service/prompt_sync_scheduler.go

@@ -0,0 +1,70 @@
+package service
+
+import (
+	"log"
+	"sync"
+
+	"github.com/basketikun/infinite-canvas/model"
+	"github.com/basketikun/infinite-canvas/repository"
+	"github.com/robfig/cron/v3"
+)
+
+const defaultPromptSyncCron = "0 3 * * *"
+
+var (
+	promptSyncCron *cron.Cron
+	promptSyncOnce sync.Once
+	promptSyncMu   sync.Mutex
+)
+
+func StartPromptSyncScheduler() {
+	promptSyncOnce.Do(func() {
+		promptSyncCron = cron.New()
+		promptSyncCron.Start()
+	})
+	RefreshPromptSyncScheduler()
+}
+
+func RefreshPromptSyncScheduler() {
+	promptSyncMu.Lock()
+	defer promptSyncMu.Unlock()
+	if promptSyncCron == nil {
+		return
+	}
+	for _, entry := range promptSyncCron.Entries() {
+		promptSyncCron.Remove(entry.ID)
+	}
+	settings, err := repository.GetSettings()
+	if err != nil {
+		log.Printf("load prompt sync setting failed err=%v", err)
+		return
+	}
+	setting := normalizePromptSyncSetting(settings.Private.PromptSync)
+	if !setting.Enabled {
+		return
+	}
+	if _, err := promptSyncCron.AddFunc(setting.Cron, SyncRemotePromptCategories); err != nil {
+		log.Printf("add prompt sync cron failed cron=%s err=%v", setting.Cron, err)
+	}
+}
+
+func SyncRemotePromptCategories() {
+	for _, category := range repository.PromptCategories() {
+		if !category.Remote {
+			continue
+		}
+		log.Printf("scheduled prompt sync start category=%s", category.Category)
+		if _, err := SyncPromptCategory(category.Category); err != nil {
+			log.Printf("scheduled prompt sync failed category=%s err=%v", category.Category, err)
+			continue
+		}
+		log.Printf("scheduled prompt sync done category=%s", category.Category)
+	}
+}
+
+func normalizePromptSyncSetting(setting model.PromptSyncSetting) model.PromptSyncSetting {
+	if setting.Cron == "" {
+		setting.Cron = defaultPromptSyncCron
+	}
+	return setting
+}