feat(core): add agentsmd-audit skill files

The previous commit only landed the research-folder rename — a multi-path
git add silently failed and left CONTEXT.md, ADR-0012, and the actual skill
files unstaged. This lands them: the agentsmd-audit skill itself (three
deterministic validators for secrets, structure, and drift against a target
repo's AGENTS.md), its bats test suite, provenance record, and the
CONTEXT.md/ADR entries documenting why this lives in core rather than
kyberforge.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plugins/core/skills/agentsmd-audit/tests/README.md

@@ -0,0 +1,30 @@
+# tests/
+
+Test files for scripts bundled with this skill.
+
+## Dependencies
+
+Tests require [bats-support](https://github.com/bats-core/bats-support) and
+[bats-assert](https://github.com/bats-core/bats-assert). The test files load
+helpers from the repo root's `tests/test_helper/`.
+
+From the repo root:
+
+```bash
+git clone https://github.com/bats-core/bats-support tests/test_helper/bats-support
+git clone https://github.com/bats-core/bats-assert tests/test_helper/bats-assert
+```
+
+Run all tests for this skill (from the repo root):
+
+```bash
+bats plugins/core/skills/agentsmd-audit/tests/
+```
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `validate-secrets.bats` | Bats test suite for `scripts/validate-secrets.sh` |
+| `validate-structure.bats` | Bats test suite for `scripts/validate-structure.sh` |
+| `validate-drift.bats` | Bats test suite for `scripts/validate-drift.sh` |