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/git-flow/skills/environment-variables.md

@@ -0,0 +1,92 @@
+# Environment Variables
+
+## Purpose
+
+Centralized reference for all git-flow environment variables and their defaults.
+
+## When to Use
+
+- Configuring git-flow behavior in `/git-config`
+- Documenting available options to users
+- Setting up project-specific overrides
+
+## Core Variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `GIT_DEFAULT_BASE` | `development` | Base branch for new branches and merges |
+| `GIT_PROTECTED_BRANCHES` | `main,master,development,staging,production` | Comma-separated list of protected branches |
+| `GIT_WORKFLOW_STYLE` | `feature-branch` | Workflow: simple, feature-branch, pr-required, trunk-based |
+
+## Commit Variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `GIT_COMMIT_STYLE` | `conventional` | Message style: conventional, simple, detailed |
+| `GIT_SIGN_COMMITS` | `false` | Use GPG signing |
+| `GIT_CO_AUTHOR` | `true` | Include Claude co-author footer |
+
+## Push/Sync Variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `GIT_AUTO_PUSH` | `false` | Auto-push after commit |
+| `GIT_PUSH_STRATEGY` | `rebase` | Handle diverged branches: rebase, merge |
+| `GIT_SYNC_STRATEGY` | `rebase` | Incorporate upstream changes: rebase, merge |
+| `GIT_AUTO_PRUNE` | `true` | Auto-prune stale remote refs on sync |
+
+## Branch Variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `GIT_BRANCH_PREFIX` | `true` | Use type/ prefix for branches |
+| `GIT_AUTO_DELETE_MERGED` | `true` | Auto-delete merged branches |
+| `GIT_AUTO_DELETE_REMOTE` | `false` | Auto-delete remote branches |
+| `GIT_CLEANUP_STALE` | `true` | Include stale branches in cleanup |
+
+## Workflow Styles
+
+### simple
+- Direct commits to main/development
+- No feature branches required
+- Best for: Solo projects, small scripts
+
+### feature-branch (Default)
+- Feature branches from development
+- Merge when complete
+- Best for: Small teams
+
+### pr-required
+- Feature branches from development
+- Requires PR for merge
+- Best for: Code review workflows
+
+### trunk-based
+- Short-lived branches (< 1 day)
+- Frequent integration
+- Best for: CI/CD heavy workflows
+
+## Storage Locations
+
+| Scope | Location | Priority |
+|-------|----------|----------|
+| Project | `.env` or `.claude/settings.json` | Highest |
+| User | `~/.config/claude/git-flow.env` | Lower |
+
+Project settings override user settings.
+
+## Example Configuration
+
+**.env file:**
+```bash
+GIT_DEFAULT_BASE=main
+GIT_WORKFLOW_STYLE=pr-required
+GIT_AUTO_DELETE_MERGED=true
+GIT_COMMIT_STYLE=conventional
+GIT_PROTECTED_BRANCHES=main,staging,production
+```
+
+## Related Skills
+
+- skills/git-safety.md
+- skills/commit-conventions.md