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>

packages/db/src/schema/index.ts

@@ -1,6 +1,7 @@
 export { companies } from "./companies.js";
 export { companyLogos } from "./company_logos.js";
 export { authUsers, authSessions, authAccounts, authVerifications } from "./auth.js";
+export { instanceSettings } from "./instance_settings.js";
 export { instanceUserRoles } from "./instance_user_roles.js";
 export { agents } from "./agents.js";
 export { companyMemberships } from "./company_memberships.js";