Root-mounted SPA custom UI broke under nested routes due route-relative assets and service-worker registration

A root-mounted web control UI was opened at a nested custom route such as /activity/chat. The built bundle registered ./sw.js, injected custom assets used ./custom.js/./custom.css, and route-inferred bootstrap/static paths requested nested URLs. Browsers reported service-worker install errors, missing custom JS/CSS/highlight bundles, CSP-blocked localhost diagnostics, and generic route-prefixed 404s.