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

backend/internal/handler/admin/setting_handler.go

@@ -235,6 +235,9 @@ func (h *SettingHandler) GetSettings(c *gin.Context) {
 		PaymentCancelRateLimitWindow:           paymentCfg.CancelRateLimitWindow,
 		PaymentCancelRateLimitUnit:             paymentCfg.CancelRateLimitUnit,
 		PaymentCancelRateLimitMode:             paymentCfg.CancelRateLimitMode,
+
+		ChannelMonitorEnabled:                settings.ChannelMonitorEnabled,
+		ChannelMonitorDefaultIntervalSeconds: settings.ChannelMonitorDefaultIntervalSeconds,
 	}
 	response.Success(c, systemSettingsResponseData(payload, authSourceDefaults))
 }
@@ -425,6 +428,10 @@ type UpdateSettingsRequest struct {
 	PaymentCancelRateLimitWindow  *int    `json:"payment_cancel_rate_limit_window"`
 	PaymentCancelRateLimitUnit    *string `json:"payment_cancel_rate_limit_unit"`
 	PaymentCancelRateLimitMode    *string `json:"payment_cancel_rate_limit_window_mode"`
+
+	// Channel Monitor feature switch
+	ChannelMonitorEnabled                *bool `json:"channel_monitor_enabled"`
+	ChannelMonitorDefaultIntervalSeconds *int  `json:"channel_monitor_default_interval_seconds"`
 }
 
 // UpdateSettings 更新系统设置
@@ -1219,6 +1226,18 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 			}
 			return previousSettings.AccountQuotaNotifyEmails
 		}(),
+		ChannelMonitorEnabled: func() bool {
+			if req.ChannelMonitorEnabled != nil {
+				return *req.ChannelMonitorEnabled
+			}
+			return previousSettings.ChannelMonitorEnabled
+		}(),
+		ChannelMonitorDefaultIntervalSeconds: func() int {
+			if req.ChannelMonitorDefaultIntervalSeconds != nil {
+				return *req.ChannelMonitorDefaultIntervalSeconds
+			}
+			return previousSettings.ChannelMonitorDefaultIntervalSeconds
+		}(),
 	}
 
 	authSourceDefaults := &service.AuthSourceDefaultSettings{
@@ -1449,6 +1468,9 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 		PaymentCancelRateLimitWindow:           updatedPaymentCfg.CancelRateLimitWindow,
 		PaymentCancelRateLimitUnit:             updatedPaymentCfg.CancelRateLimitUnit,
 		PaymentCancelRateLimitMode:             updatedPaymentCfg.CancelRateLimitMode,
+
+		ChannelMonitorEnabled:                updatedSettings.ChannelMonitorEnabled,
+		ChannelMonitorDefaultIntervalSeconds: updatedSettings.ChannelMonitorDefaultIntervalSeconds,
 	}
 	response.Success(c, systemSettingsResponseData(payload, updatedAuthSourceDefaults))
 }
@@ -1805,6 +1827,12 @@ func diffSettings(before *service.SystemSettings, after *service.SystemSettings,
 	if !equalNotifyEmailEntries(before.AccountQuotaNotifyEmails, after.AccountQuotaNotifyEmails) {
 		changed = append(changed, "account_quota_notify_emails")
 	}
+	if before.ChannelMonitorEnabled != after.ChannelMonitorEnabled {
+		changed = append(changed, "channel_monitor_enabled")
+	}
+	if before.ChannelMonitorDefaultIntervalSeconds != after.ChannelMonitorDefaultIntervalSeconds {
+		changed = append(changed, "channel_monitor_default_interval_seconds")
+	}
 	changed = appendAuthSourceDefaultChanges(changed, beforeAuthSourceDefaults, afterAuthSourceDefaults)
 	return changed
 }