fix(vpn): handle VPN forwarding mode downgrades and support runtime VPN config updates

ts/config/classes.route-config-manager.ts

@@ -73,6 +73,12 @@ export class RouteConfigManager {
     return this.routes.get(id);
   }
 
+  public setVpnClientIpsResolver(
+    resolver?: (route: IDcRouterRouteConfig, routeId?: string) => TIpAllowEntry[],
+  ): void {
+    this.getVpnClientIpsForRoute = resolver;
+  }
+
   /**
    * Load persisted routes, seed serializable config/email/dns routes,
    * compute warnings, and apply the combined DB-backed + runtime route set to SmartProxy.