Fix browser control WebSocket routing

[sppidy]

Summary

• resolve /ui/ws from the browser current origin at connection time
• remove the misleading runtime NEXT_PUBLIC_WS_URL compose setting
• log abnormal close codes and add a stale-build-URL regression test

Root cause

Durable REST/SSE and the raw production WebSocket synthetic were healthy, but browsers never reached the server. The client retained a Next.js public-environment branch whose build/runtime semantics could select a stale URL rather than the dashboard origin.

Validation

• WebSocketProvider tests: 8 passed
• TypeScript: passed
• ESLint: 0 errors (existing warnings only)
• Next.js production build: passed
• built client contains no NEXT_PUBLIC_WS_URL or placeholder WebSocket hostname

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.