Add 6 software development skills

- code-review: critical code review of uncommitted changes
- code-self-review: self-review after writing code
- code-cleanup: garbage collection for technical debt
- security-review: security review from pentester perspective
- create-merge-request: create GitLab MR from uncommitted changes
- understand-project: learn about a project from docs and structure

understand-project/SKILL.md

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+---
+name: understand-project
+description: >
+  Learn about a project from its docs, README, and structure. Provides a quick overview
+  of the tech stack, project structure, how to run it, and key conventions.
+---
+
+# Understand This Project
+
+Take a moment to familiarize yourself with this project before doing any work. Your goal is to build context so you can assist effectively.
+
+## Step 1: Find and Read Documentation
+
+Look for and read the following files (if they exist):
+
+### Primary Documentation
+- `README.md` or `README` (any case variation)
+- `docs/` directory - read key files inside
+- `CONTRIBUTING.md` - contribution guidelines
+- `ARCHITECTURE.md` or `docs/architecture.md` - system design
+
+### Configuration Files (skim for context)
+- `package.json`, `Cargo.toml`, `pyproject.toml`, `go.mod` - understand dependencies and project type
+- `.env.example` or `.env.sample` - understand required configuration
+- `Makefile`, `justfile`, or similar - understand available commands
+
+### Additional Context
+- `CHANGELOG.md` - recent changes and version history
+- `.claude/` directory - any project-specific Claude instructions
+
+## Step 2: Understand the Structure
+
+Get a high-level view of the project structure:
+- What are the main directories and their purposes?
+- What language(s) and framework(s) is this project using?
+- What's the entry point of the application?
+
+## Step 3: Report Back
+
+Once you've gathered context, provide a brief summary:
+
+### Project Overview
+- What is this project? (1-2 sentences)
+- What problem does it solve?
+
+### Tech Stack
+- Languages, frameworks, and key dependencies
+
+### Project Structure
+- Main directories and their purposes
+
+### How to Run
+- Development setup commands (if documented)
+- How to run tests (if documented)
+
+### Key Things to Know
+- Any important patterns, conventions, or gotchas mentioned in the docs
+- Areas marked as work-in-progress or known issues
+
+---
+
+Keep your summary concise but informative. After reporting, you'll be ready to assist with tasks in this codebase.