Improve connection diagnostics and recovery

[askac]

Summary

• add local-time ISO timestamps and session-scoped connection diagnostics
• restore retained terminals after browser authorization completes on a reconnected socket
• isolate browser smoke tests from the WSL/Tk access window
• make the access window closable and tie its helper process lifecycle to the launcher
• close stale access windows immediately and tolerate five transient offline polls before self-closing

Validation

• tools/.venv_wsl/bin/python -m py_compile app.py scripts/access_window.py tests/agent_backend_smoke.py tests/agent_browser_smoke.py
• tools/.venv_wsl/bin/python tests/agent_backend_smoke.py
• tools/.venv_wsl/bin/python tests/agent_browser_smoke.py
• desktop and 390px mobile diagnostics screenshot inspection
• WSL launcher normal-stop test: Windows Tk helper exited with the server
• WSL launcher SIGKILL test: Windows Tk helper self-closed after launcher polling timed out
• git diff --check

Security

• diagnostics remain session-scoped and redact URL tokens
• unauthorized sockets still receive no protected terminal information
• access-window cleanup targets only the helper process created by the current launcher