feat: add code-sentinel plugin for security scanning and refactoring

Adds security scanning via PreToolUse hooks + refactoring commands:
- PreToolUse hook catches security issues before code is written
- /security-scan command for comprehensive security audit
- /refactor command to apply refactoring patterns
- /refactor-dry command to preview refactoring opportunities
- security-reviewer agent for vulnerability analysis
- refactor-advisor agent for code structure improvements
- security-patterns skill for vulnerability detection rules

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/code-sentinel/README.md

@@ -0,0 +1,47 @@
+# code-sentinel
+
+Security scanning and code refactoring tools for Claude Code projects.
+
+## Features
+
+### Security Scanning
+- **PreToolUse Hook**: Catches vulnerabilities BEFORE code is written
+- **Full Audit**: `/security-scan` for comprehensive project review
+- **Pattern Detection**: SQL injection, XSS, command injection, secrets, and more
+
+### Refactoring
+- **Pattern Library**: Extract method, simplify conditionals, modernize syntax
+- **Safe Transforms**: Preview changes before applying
+- **Reference Updates**: Automatically updates all call sites
+
+## Commands
+
+| Command | Description |
+|---------|-------------|
+| `/security-scan` | Full project security audit |
+| `/refactor <target>` | Apply refactoring with pattern |
+| `/refactor-dry <target>` | Preview opportunities without changes |
+
+## Hooks
+
+- **PreToolUse (Write\|Edit)**: Scans code for security patterns before writing
+
+## Security Patterns Detected
+
+| Category | Examples |
+|----------|----------|
+| Injection | SQL, Command, Code (eval), XSS |
+| Secrets | Hardcoded API keys, passwords |
+| Deserialization | Pickle, unsafe YAML |
+| Path Traversal | Unsanitized file paths |
+
+## Installation
+
+```bash
+/plugin marketplace add https://gitea.hotserv.cloud/personal-projects/support-claude-mktplace.git
+/plugin install code-sentinel
+```
+
+## Integration
+
+See claude-md-integration.md for CLAUDE.md additions.