* sftp: match permission paths on path-component boundaries
Permission checks compared paths with raw string prefixes, so a
permission entry for /tenants/alice also matched sibling paths such as
/tenants/alice-archive, letting a scoped user read and overwrite
another tenant's files. The home directory containment check had the
same flaw. Route both through pathWithin, which cleans the paths and
requires exact equality or a separator-delimited descendant.
* sftp: clean permission path into a local when ranking matches