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/lib/instance-settings.ts

@@ -0,0 +1,24 @@
+export const DEFAULT_INSTANCE_SETTINGS_PATH = "/instance/settings/heartbeats";
+
+export function normalizeRememberedInstanceSettingsPath(rawPath: string | null): string {
+  if (!rawPath) return DEFAULT_INSTANCE_SETTINGS_PATH;
+
+  const match = rawPath.match(/^([^?#]*)(\?[^#]*)?(#.*)?$/);
+  const pathname = match?.[1] ?? rawPath;
+  const search = match?.[2] ?? "";
+  const hash = match?.[3] ?? "";
+
+  if (
+    pathname === "/instance/settings/heartbeats" ||
+    pathname === "/instance/settings/plugins" ||
+    pathname === "/instance/settings/experimental"
+  ) {
+    return `${pathname}${search}${hash}`;
+  }
+
+  if (/^\/instance\/settings\/plugins\/[^/?#]+$/.test(pathname)) {
+    return `${pathname}${search}${hash}`;
+  }
+
+  return DEFAULT_INSTANCE_SETTINGS_PATH;
+}