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/channelmonitorhistory/where.go

@@ -55,11 +55,6 @@ func IDLTE(id int64) predicate.ChannelMonitorHistory {
 	return predicate.ChannelMonitorHistory(sql.FieldLTE(FieldID, id))
 }
 
-// DeletedAt applies equality check predicate on the "deleted_at" field. It's identical to DeletedAtEQ.
-func DeletedAt(v time.Time) predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldEQ(FieldDeletedAt, v))
-}
-
 // MonitorID applies equality check predicate on the "monitor_id" field. It's identical to MonitorIDEQ.
 func MonitorID(v int64) predicate.ChannelMonitorHistory {
 	return predicate.ChannelMonitorHistory(sql.FieldEQ(FieldMonitorID, v))
@@ -90,56 +85,6 @@ func CheckedAt(v time.Time) predicate.ChannelMonitorHistory {
 	return predicate.ChannelMonitorHistory(sql.FieldEQ(FieldCheckedAt, v))
 }
 
-// DeletedAtEQ applies the EQ predicate on the "deleted_at" field.
-func DeletedAtEQ(v time.Time) predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldEQ(FieldDeletedAt, v))
-}
-
-// DeletedAtNEQ applies the NEQ predicate on the "deleted_at" field.
-func DeletedAtNEQ(v time.Time) predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldNEQ(FieldDeletedAt, v))
-}
-
-// DeletedAtIn applies the In predicate on the "deleted_at" field.
-func DeletedAtIn(vs ...time.Time) predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldIn(FieldDeletedAt, vs...))
-}
-
-// DeletedAtNotIn applies the NotIn predicate on the "deleted_at" field.
-func DeletedAtNotIn(vs ...time.Time) predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldNotIn(FieldDeletedAt, vs...))
-}
-
-// DeletedAtGT applies the GT predicate on the "deleted_at" field.
-func DeletedAtGT(v time.Time) predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldGT(FieldDeletedAt, v))
-}
-
-// DeletedAtGTE applies the GTE predicate on the "deleted_at" field.
-func DeletedAtGTE(v time.Time) predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldGTE(FieldDeletedAt, v))
-}
-
-// DeletedAtLT applies the LT predicate on the "deleted_at" field.
-func DeletedAtLT(v time.Time) predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldLT(FieldDeletedAt, v))
-}
-
-// DeletedAtLTE applies the LTE predicate on the "deleted_at" field.
-func DeletedAtLTE(v time.Time) predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldLTE(FieldDeletedAt, v))
-}
-
-// DeletedAtIsNil applies the IsNil predicate on the "deleted_at" field.
-func DeletedAtIsNil() predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldIsNull(FieldDeletedAt))
-}
-
-// DeletedAtNotNil applies the NotNil predicate on the "deleted_at" field.
-func DeletedAtNotNil() predicate.ChannelMonitorHistory {
-	return predicate.ChannelMonitorHistory(sql.FieldNotNull(FieldDeletedAt))
-}
-
 // MonitorIDEQ applies the EQ predicate on the "monitor_id" field.
 func MonitorIDEQ(v int64) predicate.ChannelMonitorHistory {
 	return predicate.ChannelMonitorHistory(sql.FieldEQ(FieldMonitorID, v))