chore(tests): lint rule — cap test files per production module at 2 (#3738)

* chore(tests): lint rule — cap test files per production module at 2

Adds scripts/lint-test-file-count.cjs with a ratcheted allowlist
(scripts/lint-test-file-count.allowlist.json) capturing today's
30 violating clusters as a ceiling. New entries blocked at PR time;
reductions ratchet automatically.

Wires into .github/workflows/test.yml as a new step in lint-tests.

Refs #3737

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* chore(tests): add docs-exempt to changeset fragment

Internal CI lint rule — no user-facing docs impact.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -76,6 +76,7 @@
     "lint:descriptions": "node scripts/lint-descriptions.cjs",
     "lint:skill-deps": "node scripts/lint-skill-deps.cjs",
     "lint:tests": "node scripts/lint-no-source-grep.cjs",
+    "lint:test-file-count": "node scripts/lint-test-file-count.cjs",
     "lint:pr-checks": "node scripts/lint-pr-check-project-dir.cjs",
     "lint:changeset": "node scripts/changeset/lint.cjs",
     "lint:docs": "node scripts/lint-docs-required.cjs",