feat(channel-monitor): add feature switch settings + fix extra_models save

Settings:
- New "功能开关" tab between 通用设置 and 安全与认证
- ChannelMonitorEnabled toggle: runner skips scheduling when false,
  user-facing list returns empty
- ChannelMonitorDefaultIntervalSeconds (15-3600): pre-fills interval
  when creating a new monitor; each monitor can still override

Bug fix:
- ModelTagInput now commits pending input on blur, not just Enter/Tab.
  Previously clicking "save" with an un-Enter'd extra model would drop
  the value (DB stored extra_models=[] even when user typed entries).

Backend:
- domain_constants: SettingKeyChannelMonitor{Enabled,DefaultIntervalSeconds}
- SettingService.GetChannelMonitorRuntime: lightweight getter used by
  runner tick + user handler per-request (fail-open on DB error)
- Runner tickDueChecks: bails early when feature disabled
- ChannelMonitorUserHandler: checks feature flag before serving
- Comment on runner doc: scheduler state is implicit (every tick re-reads
  ListEnabled from DB), so CRUD ops on monitors self-maintain the schedule

Bump VERSION to 0.1.114.25

frontend/src/i18n/locales/zh.ts

@@ -4695,6 +4695,7 @@ export default {
       description: '管理注册、邮箱验证、默认值和 SMTP 设置',
       tabs: {
         general: '通用设置',
+        features: '功能开关',
         security: '安全与认证',
         users: '用户默认值',
         gateway: '网关服务',
@@ -4702,6 +4703,16 @@ export default {
         backup: '数据备份',
         payment: '支付设置',
       },
+      features: {
+        channelMonitor: {
+          title: '渠道监控',
+          description: '定期对配置的渠道发起健康检查，向用户展示可用性与延迟。关闭后调度器停止扫描，用户端列表为空。',
+          enabled: '启用渠道监控',
+          enabledHint: '关闭后后台不再执行定时检测，已有数据保留。',
+          defaultInterval: '默认检测间隔（秒）',
+          defaultIntervalHint: '新建渠道监控时表单的默认值，可被单个渠道覆盖。范围 15 – 3600 秒。',
+        },
+      },
       emailTabDisabledTitle: '邮箱验证未启用',
       emailTabDisabledHint: '请在「安全与认证」选项卡中启用邮箱验证后，再配置 SMTP 设置。',
       registration: {