refactor: 文件行数超标拆解（7个文件→14个文件，全部≤200行）

- 移动本地接口定义到 interfaces.go 和 admin/interfaces.go
- favorite_controller.go → favorite_item_controller.go
- space_controller.go → space_loaders.go
- settings_controller.go → settings_api_audit.go
- admin_energy_controller.go → admin_energy_api_controller.go
- admin_post_controller.go → admin_post_action_controller.go
- comment_repo.go → comment_mention_repo.go
- post_repo.go → post_stats_repo.go

internal/controller/settings_api_notify.go

@@ -9,12 +9,6 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
-// notifyPrefReader 通知偏好读写的接口（ISP）
-type notifyPrefReader interface {
-	GetNotifyPrefs(userID uint) (map[string]bool, error)
-	UpdateNotifyPref(userID uint, key string, enabled bool) error
-}
-
 // SetNotifyPrefReader 注入通知偏好读写器
 func (sc *SettingsController) SetNotifyPrefReader(reader notifyPrefReader) {
 	sc.notifyPrefReader = reader