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/posture/SKILL.md

@@ -0,0 +1,54 @@
+---
+name: security-posture
+description: Quick security posture assessment — scorecard with grade, coverage status, and top recommendations
+---
+
+# Security Posture
+
+Quick security scorecard — grade, coverage, top recommendations. Deterministic scanner, <2 sec.
+
+## Step 1: Resolve Plugin Root
+
+Plugin root = the directory containing `plugin.json`, found by searching up from this file's location.
+
+## Step 2: Run Scanner
+
+```bash
+node <plugin-root>/scanners/posture-scanner.mjs $ARGUMENTS
+```
+
+If `$ARGUMENTS` is empty, scan the current working directory.
+
+Parse the JSON output: `scoring.grade` (A-F), `scoring.pass_rate`, `risk.score` (0-100), `risk.band`, `risk.verdict`, `categories[]`, `findings[]`, `counts`.
+
+## Step 3: Format Scorecard
+
+```
+# Security Posture — [project name]
+
+| Field | Value |
+|-------|-------|
+| **Grade** | [A-F] |
+| **Risk Score** | [N]/100 ([band]) |
+| **Verdict** | [verdict] |
+
+## Category Scorecard
+
+| # | Category | Status | Findings |
+|---|----------|--------|----------|
+[one row per category, status as PASS/PARTIAL/FAIL/N-A]
+
+## Top Findings
+
+[List critical and high findings with title and recommendation]
+
+## Quick Wins
+
+[List low-effort fixes from findings]
+```
+
+## Step 4: Closing
+
+- Grade A/B: "Posture solid. Re-run after major changes."
+- Grade C: "Run the audit skill for detailed findings."
+- Grade D/F: "Significant exposure. Run audit before production use."