feat(llm-security-copilot): port llm-security v5.1.0 to GitHub Copilot CLI

Full port of llm-security plugin for internal use on Windows with GitHub
Copilot CLI. Protocol translation layer (copilot-hook-runner.mjs)
normalizes Copilot camelCase I/O to Claude Code snake_case format — all
original hook scripts run unmodified.

- 8 hooks with protocol translation (stdin/stdout/exit code)
- 18 SKILL.md skills (Agent Skills Open Standard)
- 6 .agent.md agent definitions
- 20 scanners + 14 scanner lib modules (unchanged)
- 14 knowledge files (unchanged)
- 39 test files including copilot-port-verify.mjs (17 tests)
- Windows-ready: node:path, os.tmpdir(), process.execPath, no bash

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

plugins/llm-security-copilot/skills/registry/SKILL.md

@@ -0,0 +1,53 @@
+---
+name: security-registry
+description: Skill signature registry — view stats, scan and register skills, search known fingerprints
+---
+
+# Skill Registry
+
+Track scanned skills by fingerprint. Three sub-commands.
+
+## Sub-command: Stats (default)
+
+```bash
+node -e "
+import { getStats, listEntries } from '<plugin-root>/scanners/lib/skill-registry.mjs';
+const stats = getStats('<plugin-root>');
+const entries = listEntries('<plugin-root>', 5);
+console.log(JSON.stringify({ stats, entries }));
+" --input-type=module
+```
+
+Show: total entries, last scan date, 5 most recent entries.
+
+## Sub-command: Scan
+
+```bash
+node -e "
+import { fingerprintSkill, checkRegistry } from '<plugin-root>/scanners/lib/skill-registry.mjs';
+const r = fingerprintSkill('<target>');
+const c = checkRegistry(r.fingerprint, '<plugin-root>');
+console.log(JSON.stringify({ fingerprint: r.fingerprint, name: r.name, files: r.files, ...c }));
+" --input-type=module
+```
+
+If cached and not stale: show cached result. If miss or stale: run full scan, then register:
+
+```bash
+node -e "
+import { registerScan } from '<plugin-root>/scanners/lib/skill-registry.mjs';
+registerScan({ skillPath: '<target>', fingerprint: '<fp>', name: '<name>', files: <files>, verdict: '<v>', risk_score: <n>, counts: <counts>, files_scanned: <n> }, '<plugin-root>');
+" --input-type=module
+```
+
+## Sub-command: Search
+
+```bash
+node -e "
+import { searchRegistry } from '<plugin-root>/scanners/lib/skill-registry.mjs';
+const results = searchRegistry('<pattern>', '<plugin-root>');
+console.log(JSON.stringify(results));
+" --input-type=module
+```
+
+Show matching entries with verdict, risk score, last scanned date.