1ca4913291
- Add ACL structures: - VfsAceType (Allow/Deny/Audit/Alarm) - VfsAceFlag (inheritance flags) - VfsAceMask (permission masks) - VfsAce (access control entry) - VfsAcl (ACL list with default_acl) - Add VfsBackend methods: - get_acl() - retrieve ACL from .acl JSON - set_acl() - store ACL as .acl JSON - check_acl() - check permission for principal - add_ace() - add ACE to ACL - remove_ace() - remove ACE by index - LocalFs implementation: - VfsAclMeta serialization struct - ACL stored as JSON metadata (similar to quota/snapshot) - Box<VfsAcl> for recursive default_acl - Foundation for SMB/NFSv4 ACL support All 229 tests pass.