fix(studio): recover built-in Codex sessions after idle timeouts

[zakahan]

Summary

• rotate aging Codex app-server WebSocket transports before the gateway 30-minute lifetime and resume the active thread
• validate cached Codex transports when users re-enter a Sandbox session
• route Sandbox same-origin HTTP and SSE requests through the shared Studio authentication recovery flow
• retry the original request after OAuth reauthentication instead of parsing a redirected login page as an empty SSE response
• add regression coverage for transport reconnection, OAuth redirects, and confirmed 401 responses

Testing

• cd frontend && npm test — 614 tests passed
• cd frontend && npm run build
• uv run --group dev pytest -q tests/cli/test_codex_app_server.py tests/cli/test_frontend_sandbox.py — 61 tests passed
• uv run ruff check veadk/cli/codex_app_server.py veadk/cli/frontend_sandbox.py tests/cli/test_codex_app_server.py tests/cli/test_frontend_sandbox.py
• targeted pre-commit hooks and secret scan

Manual validation

• deploy the fork branch and expire the Studio OAuth session during a Sandbox conversation
• confirm reauthentication retries the pending message without an empty-reply error
• leave a Codex session open for at least 20 minutes and confirm the next message resumes the same thread without a gateway WebSocket lifetime error

Notes

• Draft pending deployed-environment validation.
• Pyright was not available in the current development environment.