fix(channel-monitor): drop soft delete, refactor feature flag to declarative form

### 后端修复：日志表不该用软删除

channel_monitor_histories / channel_monitor_daily_rollups 都是日志/聚合表，
没有恢复需求。110 里加的 SoftDeleteMixin 会让 DELETE 自动变成 UPDATE deleted_at，
导致行和索引只增不减，徒增磁盘占用和查询成本。

改回分批物理删（参考 OpsCleanupService.deleteOldRowsByID 模板）：

- ent schema 移除 SoftDeleteMixin，重新 go generate
- repo 新增 deleteChannelMonitorBatched 辅助 + 两条 prune SQL 常量
  （WITH batch AS SELECT id LIMIT 5000 → DELETE IN batch）
- DeleteHistoryBefore / DeleteRollupsBefore 改调分批 raw SQL
- 移除 ComputeAvailability / ComputeAvailabilityForMonitors / UpsertDailyRollupsFor /
  ListLatestPerModel / ListLatestForMonitorIDs / ListRecentHistoryForMonitors 等
  raw SQL 中的 deleted_at IS NULL 过滤
- UpsertDailyRollupsFor 的 ON CONFLICT 去掉 deleted_at = NULL 重置
- migration 111 DROP COLUMN deleted_at + 对应索引（110 已部署但 maintenance
  首跑在次日 02:00，此时尚无业务数据在依赖软删除）

### 前端重构：feature flag 声明式 + 复用

AppSidebar.vue 里 7 处 `...(flag ? [item] : [])` 样板代码删光，改为 NavItem 加
featureFlag?: () => boolean | undefined 字段，加一个 applyFeatureFlags 递归
过滤（含 children）。语义统一为 `!== false`（宽容策略，undefined 时默认显示，
避免 public settings 未加载完成时菜单闪烁消失 — 对应用户反馈"刷新后菜单消失
要去保存设置才回来"）。

- 集中声明 4 个 flag getter：flagChannelMonitor / flagPayment /
  flagOpsMonitoring / flagAdminPayment
- 提取 buildSelfNavItems 复用用户端主菜单和管理员"我的账户"子菜单
- 未来新增开关：在统一位置加一个 flag getter + 给对应 NavItem 加字段
  （不用再动渲染逻辑）

bump 0.1.114.29

backend/ent/client.go

@@ -1912,14 +1912,12 @@ func (c *ChannelMonitorDailyRollupClient) QueryMonitor(_m *ChannelMonitorDailyRo
 
 // Hooks returns the client hooks.
 func (c *ChannelMonitorDailyRollupClient) Hooks() []Hook {
-	hooks := c.hooks.ChannelMonitorDailyRollup
-	return append(hooks[:len(hooks):len(hooks)], channelmonitordailyrollup.Hooks[:]...)
+	return c.hooks.ChannelMonitorDailyRollup
 }
 
 // Interceptors returns the client interceptors.
 func (c *ChannelMonitorDailyRollupClient) Interceptors() []Interceptor {
-	inters := c.inters.ChannelMonitorDailyRollup
-	return append(inters[:len(inters):len(inters)], channelmonitordailyrollup.Interceptors[:]...)
+	return c.inters.ChannelMonitorDailyRollup
 }
 
 func (c *ChannelMonitorDailyRollupClient) mutate(ctx context.Context, m *ChannelMonitorDailyRollupMutation) (Value, error) {
@@ -2063,14 +2061,12 @@ func (c *ChannelMonitorHistoryClient) QueryMonitor(_m *ChannelMonitorHistory) *C
 
 // Hooks returns the client hooks.
 func (c *ChannelMonitorHistoryClient) Hooks() []Hook {
-	hooks := c.hooks.ChannelMonitorHistory
-	return append(hooks[:len(hooks):len(hooks)], channelmonitorhistory.Hooks[:]...)
+	return c.hooks.ChannelMonitorHistory
 }
 
 // Interceptors returns the client interceptors.
 func (c *ChannelMonitorHistoryClient) Interceptors() []Interceptor {
-	inters := c.inters.ChannelMonitorHistory
-	return append(inters[:len(inters):len(inters)], channelmonitorhistory.Interceptors[:]...)
+	return c.inters.ChannelMonitorHistory
 }
 
 func (c *ChannelMonitorHistoryClient) mutate(ctx context.Context, m *ChannelMonitorHistoryMutation) (Value, error) {