Drop the archived old/ tree, root AI notes, splashgame.md (Arcade lives
in the private sandbox), widgets-dll leftovers, and LAN/oracle helper
scripts. Move download_*.sh into tools/, and move sim/math out of
libs/game/ so the public repo no longer has a game/ directory.
Also quiet first-party compile noise and skip asset-ui tests that need
sandbox kits or uncommitted fixtures.
hotload_ui and xr pulled a dylib widgets wrapper that made
`cargo build --workspace` fail. XR now uses normal widgets.
The vendored weezl async test needed tokio, which we do not ship.
