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/scripts/validate-secrets.sh

@@ -0,0 +1,120 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+usage() {
+  cat <<EOF
+Usage: validate-secrets.sh <repo-root>
+
+Scan every AGENTS.md file in a repo (root and nested) for embedded secrets,
+API keys, tokens, or connection strings. AGENTS.md is committed content —
+real credentials in it are a hard-prohibition violation, not a style nit.
+Placeholders (<your-key>, \$ENV_VAR, YOUR_TOKEN_HERE, example.com, etc.) are
+not flagged.
+
+Arguments:
+  repo-root  Path to the repository root to scan.
+
+Exit codes:
+  0  No findings
+  1  One or more FAIL findings
+EOF
+}
+
+if [[ "${1:-}" == "--help" || "${1:-}" == "-h" ]]; then
+  usage
+  exit 0
+fi
+
+if [[ $# -lt 1 ]]; then
+  echo "Error: repo-root is required." >&2
+  echo "" >&2
+  usage >&2
+  exit 1
+fi
+
+python3 -u - "$1" <<'PYTHON'
+import sys
+import os
+import re
+
+repo_root = os.path.abspath(sys.argv[1])
+if not os.path.isdir(repo_root):
+    print(f"Error: '{repo_root}' is not a directory.", file=sys.stderr)
+    sys.exit(1)
+
+EXCLUDE_DIRS = {".git", "node_modules", "vendor", ".venv", "venv", "dist", "build"}
+
+def find_agents_md(root):
+    results = []
+    for dirpath, dirnames, filenames in os.walk(root):
+        dirnames[:] = [d for d in dirnames if d not in EXCLUDE_DIRS and not d.startswith(".")]
+        for fname in filenames:
+            if fname == "AGENTS.md":
+                results.append(os.path.join(dirpath, fname))
+    return sorted(results)
+
+PLACEHOLDER_RE = re.compile(
+    r'(?i)(your[_-]|my[_-]|example|xxx+|placeholder|changeme|<[^>]+>|\$\{|\$[A-Z_][A-Z0-9_]*|\.\.\.|redacted)'
+)
+
+PATTERNS = [
+    ("AWS access key ID", re.compile(r'AKIA[0-9A-Z]{16}')),
+    ("Private key block", re.compile(r'-----BEGIN [A-Z ]*PRIVATE KEY-----')),
+    ("GitHub token", re.compile(r'gh[pousr]_[A-Za-z0-9]{36,}')),
+    ("Slack token", re.compile(r'xox[baprs]-[A-Za-z0-9-]{10,}')),
+    ("GitLab token", re.compile(r'glpat-[A-Za-z0-9_-]{20,}')),
+    ("Generic API-style secret token", re.compile(r'\bsk-[A-Za-z0-9]{20,}\b')),
+    (
+        "Credential-bearing connection string",
+        re.compile(r'[a-zA-Z][a-zA-Z0-9+.-]*://[^:@/\s]+:[^@/\s]+@[^\s\'"]+'),
+    ),
+    (
+        "Assigned secret/password/token literal",
+        re.compile(
+            r'(?i)\b(api[_-]?key|secret|token|password|passwd|pwd|access[_-]?key)\b'
+            r'\s*[:=]\s*[\'"]?([A-Za-z0-9+/_.\-]{12,})[\'"]?'
+        ),
+    ),
+]
+
+findings = []
+
+def emit_fail(desc, fpath, lineno, why, fix):
+    findings.append((desc, fpath, lineno, why, fix))
+
+for fpath in find_agents_md(repo_root):
+    rel = os.path.relpath(fpath, repo_root)
+    with open(fpath, encoding="utf-8", errors="replace") as f:
+        lines = f.readlines()
+    for i, line in enumerate(lines, start=1):
+        if PLACEHOLDER_RE.search(line):
+            continue
+        for label, pattern in PATTERNS:
+            m = pattern.search(line)
+            if not m:
+                continue
+            # Re-check placeholder allowlist against just the matched value, in case
+            # the placeholder marker sits outside the regex's own match span.
+            value = m.group(0)
+            if PLACEHOLDER_RE.search(value):
+                continue
+            emit_fail(
+                f"Possible {label}",
+                f"{rel}:{i}",
+                i,
+                "AGENTS.md is committed content; this line matches a real-looking credential pattern rather than a placeholder.",
+                "Remove the embedded credential and replace it with an environment variable reference or placeholder (e.g. $API_KEY, <your-token>).",
+            )
+            break
+
+if not findings:
+    sys.exit(0)
+
+for desc, fpath, _lineno, why, fix in findings:
+    print(f"FAIL  {desc} — {fpath}")
+    print(f"      Why: {why}")
+    print(f"      Fix: {fix}")
+    print()
+
+sys.exit(1)
+PYTHON