refactor: extract skills from commands across 8 plugins

Refactored commands to extract reusable skills following the
Commands → Skills separation pattern. Each command is now <50 lines
and references skill files for detailed knowledge.

Plugins refactored:
- claude-config-maintainer: 5 commands → 7 skills
- code-sentinel: 3 commands → 2 skills
- contract-validator: 5 commands → 6 skills
- data-platform: 10 commands → 6 skills
- doc-guardian: 5 commands → 6 skills (replaced nested dir)
- git-flow: 8 commands → 7 skills

Skills contain: workflows, validation rules, conventions,
reference data, tool documentation

Commands now contain: YAML frontmatter, agent assignment,
skills list, brief workflow steps, parameters

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

plugins/claude-config-maintainer/skills/claude-md-structure.md

@@ -0,0 +1,113 @@
+# CLAUDE.md Structure Reference
+
+This skill defines the standard structure, required sections, and templates for CLAUDE.md files.
+
+## Required Sections
+
+Every CLAUDE.md MUST have these sections:
+
+| Section | Purpose | Priority |
+|---------|---------|----------|
+| Project Overview | What the project does | Required |
+| Quick Start | Build/test/run commands | Required |
+| Critical Rules | Must-follow constraints | Required |
+| Pre-Change Protocol | Dependency check before edits | **MANDATORY** |
+
+## Recommended Sections
+
+| Section | When to Include |
+|---------|-----------------|
+| Architecture | Complex projects with multiple components |
+| Common Operations | Projects with repetitive tasks |
+| File Structure | Large codebases |
+| Troubleshooting | Projects with known gotchas |
+| Integration Points | Projects with external dependencies |
+
+## Header Hierarchy
+
+```
+# CLAUDE.md (H1 - only one)
+## Section (H2 - main sections)
+### Subsection (H3 - within sections)
+#### Detail (H4 - rarely needed)
+```
+
+**Rules:**
+- Never skip levels (no H3 before H2)
+- Maximum depth: 4 levels
+- No orphaned content before first header
+
+## Templates
+
+### Minimal Template
+For small projects:
+```markdown
+# CLAUDE.md
+
+## Project Overview
+[Description]
+
+## Quick Start
+[Commands]
+
+## Critical Rules
+[Constraints]
+
+## Pre-Change Protocol
+[Mandatory section - see pre-change-protocol.md]
+```
+
+### Standard Template (Default)
+```markdown
+# CLAUDE.md
+
+## Project Overview
+## Quick Start
+## Architecture
+## Critical Rules
+## Pre-Change Protocol
+## Common Operations
+## File Structure
+```
+
+### Comprehensive Template
+For large projects - adds:
+- Detailed Architecture
+- Troubleshooting
+- Integration Points
+- Development Workflow
+- Deployment Notes
+
+## Auto-Detection Signals
+
+| Technology | Detection Method |
+|------------|------------------|
+| Language | File extensions, config files |
+| Framework | package.json, requirements.txt, Cargo.toml |
+| Build system | Makefile, scripts in package.json |
+| Testing | pytest.ini, jest.config.js, go.mod |
+| Docker | Dockerfile, docker-compose.yml |
+| Database | ORM configs, connection strings |
+
+## Section Content Guidelines
+
+### Project Overview
+- 1-3 sentences describing purpose
+- Target audience if relevant
+- Key technologies used
+
+### Quick Start
+- Install command
+- Test command
+- Run command
+- Each with brief inline comment
+
+### Critical Rules
+- Numbered or bulleted list
+- Specific, actionable constraints
+- Include rationale for non-obvious rules
+
+### Architecture
+- High-level component diagram (ASCII or description)
+- Data flow explanation
+- Key file/directory purposes