The archive page's data (/admin/api/archive[-settings], get/delete/file) was
proxied to the GIL-busy engine, so it hung during generation. codai/api/archive.py
is torch-free and pure on-disk, so the front now serves these directly via
archive_manager (configured from config.archive), with disk scans run in a
thread. The engine's archive handlers are now dead (front handles before the
catch-all) and can be stripped in a later cleanup.

Verified: list/settings/get(404) via TestClient.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011DDv7BchtZQWsnPG6Jm49m