Add instance experimental setting for isolated workspaces

Introduce a singleton instance_settings store and experimental settings API, add the Experimental instance settings page, and gate execution workspace behavior behind the new enableIsolatedWorkspaces flag.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/app.ts

@@ -22,6 +22,7 @@ import { costRoutes } from "./routes/costs.js";
 import { activityRoutes } from "./routes/activity.js";
 import { dashboardRoutes } from "./routes/dashboard.js";
 import { sidebarBadgeRoutes } from "./routes/sidebar-badges.js";
+import { instanceSettingsRoutes } from "./routes/instance-settings.js";
 import { llmRoutes } from "./routes/llms.js";
 import { assetRoutes } from "./routes/assets.js";
 import { accessRoutes } from "./routes/access.js";
@@ -147,6 +148,7 @@ export async function createApp(
   api.use(activityRoutes(db));
   api.use(dashboardRoutes(db));
   api.use(sidebarBadgeRoutes(db));
+  api.use(instanceSettingsRoutes(db));
   const hostServicesDisposers = new Map<string, () => void>();
   const workerManager = createPluginWorkerManager();
   const pluginRegistry = pluginRegistryService(db);