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>

ui/src/App.tsx

@@ -25,6 +25,7 @@ import { Inbox } from "./pages/Inbox";
 import { CompanySettings } from "./pages/CompanySettings";
 import { DesignGuide } from "./pages/DesignGuide";
 import { InstanceSettings } from "./pages/InstanceSettings";
+import { InstanceExperimentalSettings } from "./pages/InstanceExperimentalSettings";
 import { PluginManager } from "./pages/PluginManager";
 import { PluginSettings } from "./pages/PluginSettings";
 import { PluginPage } from "./pages/PluginPage";
@@ -307,6 +308,7 @@ export function App() {
           <Route path="instance/settings" element={<Layout />}>
             <Route index element={<Navigate to="heartbeats" replace />} />
             <Route path="heartbeats" element={<InstanceSettings />} />
+            <Route path="experimental" element={<InstanceExperimentalSettings />} />
             <Route path="plugins" element={<PluginManager />} />
             <Route path="plugins/:pluginId" element={<PluginSettings />} />
           </Route>