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/diff/SKILL.md

@@ -0,0 +1,43 @@
+---
+name: security-diff
+description: Compare scan results against a stored baseline — shows new, resolved, unchanged, and moved findings
+---
+
+# Security Diff
+
+Compare current scan against a stored baseline to track security changes over time.
+
+## Step 1: Check Baseline
+
+Check if a baseline exists:
+```bash
+ls <plugin-root>/reports/baselines/
+```
+
+If no baselines exist, this is a first run — the scan will create the initial baseline.
+
+## Step 2: Run Scan with Baseline
+
+```bash
+node <plugin-root>/scanners/scan-orchestrator.mjs "<target>" --baseline --save-baseline
+```
+
+Target = `$ARGUMENTS` or current working directory.
+
+## Step 3: Display Results
+
+**First run (no prior baseline):** Show baseline created summary with finding counts.
+
+**Subsequent runs:** Parse diff output showing:
+- **New** findings (not in baseline)
+- **Resolved** findings (in baseline but not current)
+- **Moved** findings (same finding, different location)
+- **Unchanged** findings (same as baseline)
+
+Format as tables for each category.
+
+## Step 4: Advisory
+
+- All resolved, no new: "Security improving."
+- New findings detected: "Regression detected. Review new findings."
+- No changes: "Stable. No security changes since last baseline."