Gate-found (Codex CORE, repro'd): a hardlink at a clean *.md page name can
carry an arbitrary inode (incl. one outside the wiki) through the O_NOFOLLOW +
inode-identity read check — O_NOFOLLOW does not block hardlinks. Reject any
page file with st_nlink > 1 in BOTH the allowlist walk and the read-path
revalidation. Pre-existing on master (the inode recapture predates this PR's
cache); closing it here while on the read path. +1 toothed regression test
(prime cache -> hardlink listed page to outside secret -> assert 404, no leak).
Co-authored-by: rodboev <rodboev@users.noreply.github.com>
