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/channelmonitorhistory.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"time"
 
-	"entgo.io/ent"
 	"entgo.io/ent/dialect/sql"
 	"entgo.io/ent/dialect/sql/sqlgraph"
 )
@@ -16,8 +15,6 @@ const (
 	Label = "channel_monitor_history"
 	// FieldID holds the string denoting the id field in the database.
 	FieldID = "id"
-	// FieldDeletedAt holds the string denoting the deleted_at field in the database.
-	FieldDeletedAt = "deleted_at"
 	// FieldMonitorID holds the string denoting the monitor_id field in the database.
 	FieldMonitorID = "monitor_id"
 	// FieldModel holds the string denoting the model field in the database.
@@ -48,7 +45,6 @@ const (
 // Columns holds all SQL columns for channelmonitorhistory fields.
 var Columns = []string{
 	FieldID,
-	FieldDeletedAt,
 	FieldMonitorID,
 	FieldModel,
 	FieldStatus,
@@ -68,14 +64,7 @@ func ValidColumn(column string) bool {
 	return false
 }
 
-// Note that the variables below are initialized by the runtime
-// package on the initialization of the application. Therefore,
-// it should be imported in the main as follows:
-//
-//	import _ "github.com/Wei-Shaw/sub2api/ent/runtime"
 var (
-	Hooks        [1]ent.Hook
-	Interceptors [1]ent.Interceptor
 	// ModelValidator is a validator for the "model" field. It is called by the builders before save.
 	ModelValidator func(string) error
 	// DefaultMessage holds the default value on creation for the "message" field.
@@ -119,11 +108,6 @@ func ByID(opts ...sql.OrderTermOption) OrderOption {
 	return sql.OrderByField(FieldID, opts...).ToFunc()
 }
 
-// ByDeletedAt orders the results by the deleted_at field.
-func ByDeletedAt(opts ...sql.OrderTermOption) OrderOption {
-	return sql.OrderByField(FieldDeletedAt, opts...).ToFunc()
-}
-
 // ByMonitorID orders the results by the monitor_id field.
 func ByMonitorID(opts ...sql.OrderTermOption) OrderOption {
 	return sql.OrderByField(FieldMonitorID, opts...).ToFunc()