fix(docs): allowlist docs/CHANGELOG.md root-relative links for doc-release gate (cp-fhq3)

The docs/CHANGELOG.md mirror is kept byte-identical to root CHANGELOG.md
(pre-push gate #36). Its three 3.1.0 links (docs/3.1.md, README.md,
docs/install-day2-ops.md) are root-relative and resolve one level too deep
in the docs/ copy, failing the release link gate at the v3.1.0 tagged tree.
The sync invariant forbids rewriting them in the mirror, so allowlist them.
Targets verified present at repo root. Unblocks the v3.1.0 Release Publisher.

Author: boshu2

tests/docs/broken-links-allowlist.txt

@@ -124,3 +124,13 @@ skills-codex/review/references/DEEP_SCAN.md:references/TOOLS.md
 GOALS.md:.agents/research/2026-05-15-cdlc-dojo-doctrine.md
 docs/architecture/operating-loop.md:../../.agents/research/2026-05-15-cdlc-dojo-doctrine.md
 docs/cdlc.md:../.agents/research/2026-05-15-cdlc-dojo-doctrine.md
+
+# docs/CHANGELOG.md is kept byte-identical to the repo-root CHANGELOG.md
+# (pre-push gate #36: diff -q CHANGELOG.md docs/CHANGELOG.md). Its links are
+# root-relative so they resolve correctly in the canonical root copy; in the
+# docs/ mirror they resolve one level too deep. The sync invariant forbids
+# rewriting them in the mirror, so the mirror's root-relative targets are
+# allowlisted here. Targets verified to exist at repo root.
+docs/CHANGELOG.md:docs/3.1.md
+docs/CHANGELOG.md:README.md
+docs/CHANGELOG.md:docs/install-day2-ops.md