Integrates Packages 3-5 over a single shared CubeStore, the literal
CUBELinux premise (data addressed by coordinate, not path). Adds the
cubesys crate (lib + cube CLI + cube-demo) proving two end-to-end
properties: a cubefs path IS a runnable code cell at the same coordinate,
and a sealed record reopens and runs on the same store.
Two latent cross-crate bugs surfaced and fixed while integrating:
- cubecoords: refresh_flags() now preserves out-of-band flag bits
(8..=15), so cubecrypt's HEADER_FLAG_ENCRYPTED survives refresh.
- cubestore: record codec now serializes raw flag bits (TLV tag 12) so
the encrypted bit survives the store round-trip.
All gates green (./check, incl. cubefs --features mount).
XTS was previously covered only by a deleted throwaway example. Fold the
verification into the committed suite so it runs under ./check: 16-multiple
roundtrip, short-plaintext pad/strip roundtrip, multi-block sector, and the
correct non-AEAD wrong-key property (wrong key opens to different garbage).
CUBELinux-2