- TenantRegistry gains a true single-store 'shared' mode so the legacy
--store PATH invocation (and stress.sh / old cubec) keeps serving one
global store, while still parsing HELLO frames.
- cube-server now holds an Arc<TenantRegistry>, resolves each connection to
its tenant's TenantSession, and stamps the client identity from
HELLO <tenant> <owner_local> [<owner_remote>].
- Add --tenant-dir DIR for real per-tenant disk isolation (opt-in).
- Add TenantIdentity + TenantRegistry::parse_hello and a shared-session
integration test.
CUBELinux-2
50c1b55f71