* fix(frontend): reset new chat on client-side navigation
Drive the chat reset effect with Next.js's reactive pathname instead of the render-time window.location-derived flag.
During App Router transitions, window.location may still point to the previous thread until commit, leaving chat state stale until another UI interaction triggers a render. Preserve the stale 'new' param guard so created thread UUIDs are not overwritten.
* test(frontend): add e2e to cover history-only new chat reset
* docs(frontend): clarify new chat pathname synchronization