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/commands/commit-merge.md

@@ -1,94 +1,49 @@
+---
+name: commit-merge
+description: Commit current changes and merge branch into target
+agent: git-assistant
+---
+
 # /commit-merge - Commit and Merge
 
-## Visual Output
+## Skills
 
-When executing this command, display the plugin header:
-
-```
-┌──────────────────────────────────────────────────────────────────┐
-│  🔀 GIT-FLOW · Commit & Merge                                     │
-└──────────────────────────────────────────────────────────────────┘
-```
-
-Then proceed with the workflow.
+- skills/visual-header.md
+- skills/commit-conventions.md
+- skills/merge-workflow.md
+- skills/git-safety.md
+- skills/environment-variables.md
 
 ## Purpose
 
 Commit current changes, then merge the current branch into a target branch.
 
-## Behavior
+## Parameters
 
-### Step 1: Run /commit
+| Parameter | Description |
+|-----------|-------------|
+| `--target` | Target branch (default: GIT_DEFAULT_BASE) |
+| `--squash` | Squash commits on merge |
+| `--no-delete` | Keep branch after merge |
 
-Execute the standard commit workflow.
+## Workflow
 
-### Step 2: Identify Target Branch
-
-Check environment or ask:
-
-```
-Merge into which branch?
-1. development (Recommended - GIT_DEFAULT_BASE)
-2. main
-3. Other: ____
-```
-
-### Step 3: Merge Strategy
-
-```
-How should I merge?
-1. Merge commit (preserves history)
-2. Squash and merge (single commit)
-3. Rebase (linear history)
-```
-
-### Step 4: Execute Merge
-
-```bash
-# Switch to target
-git checkout <target>
-
-# Pull latest
-git pull origin <target>
-
-# Merge feature branch
-git merge <feature-branch> [--squash] [--no-ff]
-
-# Push
-git push origin <target>
-```
-
-### Step 5: Cleanup (Optional)
-
-```
-Merge complete. Delete the feature branch?
-1. Yes, delete local and remote (Recommended)
-2. Delete local only
-3. Keep the branch
-```
-
-## Environment Variables
-
-| Variable | Default | Description |
-|----------|---------|-------------|
-| `GIT_DEFAULT_BASE` | `development` | Default branch to merge into |
-| `GIT_MERGE_STRATEGY` | `merge` | Default merge strategy |
-| `GIT_AUTO_DELETE_MERGED` | `true` | Auto-delete merged branches |
-
-## Safety Checks
-
-- Verify target branch exists
-- Check for uncommitted changes before switching
-- Ensure merge doesn't conflict (preview first)
+1. **Display header** - Show GIT-FLOW Commit & Merge header
+2. **Run /commit** - Execute standard commit workflow
+3. **Identify target** - Prompt for target branch if not specified
+4. **Select strategy** - Merge commit, squash, or rebase (per merge-workflow.md)
+5. **Execute merge** - Switch to target, pull, merge, push
+6. **Handle conflicts** - Guide resolution if needed
+7. **Cleanup** - Offer to delete merged branch (per git-safety.md)
+8. **Report** - Show merge summary
 
 ## Output
 
-On success:
 ```
 Committed: abc1234
 feat(auth): add password reset functionality
 
-Merged feat/password-reset → development
+Merged feat/password-reset -> development
 Deleted branch: feat/password-reset
 
 development is now at: def5678