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/doc-guardian/skills/sync-workflow.md

@@ -0,0 +1,109 @@
+---
+name: sync-workflow
+description: Documentation synchronization process and queue management
+---
+
+# Sync Workflow
+
+## Purpose
+
+Defines how to synchronize documentation with code changes.
+
+## When to Use
+
+- **doc-sync**: Apply pending documentation updates
+- **PostToolUse hook**: Queue drift for later sync
+
+---
+
+## Queue File
+
+Location: `.doc-guardian-queue` in project root
+
+Format:
+```
+# Doc Guardian Queue
+# Generated: YYYY-MM-DD HH:MM:SS
+
+## Pending Updates
+- README.md:45 | reference | calculate_total -> compute_total
+- CLAUDE.md:23 | version | Python 3.9 -> 3.11
+- src/api/README.md:12 | path | old/path.py -> new/path.py
+```
+
+---
+
+## Update Types
+
+### Reference Fixes
+- Renamed function/class: update all doc references
+- Changed signature: update parameter documentation
+- Removed item: remove or mark deprecated in docs
+
+### Content Sync
+- Version numbers (Python, Node, dependencies)
+- Configuration keys/values
+- File paths and directory structures
+- Command examples and outputs
+
+### Structural
+- Add missing sections for new features
+- Remove sections for deleted features
+- Reorder to match current code organization
+
+---
+
+## Sync Process
+
+1. **Review Queue**
+   - Read `.doc-guardian-queue`
+   - List all pending items
+
+2. **Batch Updates**
+   - Apply each update
+   - Track in change list
+
+3. **Commit Strategy**
+   - Stage all doc changes together
+   - Single commit: `docs: sync documentation with code changes`
+   - Include summary in commit body
+
+4. **Clear Queue**
+   ```bash
+   echo "# Doc Guardian Queue - cleared after sync on $(date +%Y-%m-%d)" > .doc-guardian-queue
+   ```
+
+---
+
+## Output Format
+
+```
+## Documentation Sync Complete
+
+### Files Updated
+- README.md (3 changes)
+- CLAUDE.md (1 change)
+- src/api/README.md (2 changes)
+
+### Changes Applied
+- Updated function reference: calculate_total -> compute_total
+- Updated Python version: 3.9 -> 3.11
+- Added docstring to create_order()
+
+Committed: abc123f
+```
+
+---
+
+## Queue Entry Format
+
+```
+<file>:<line> | <type> | <old> -> <new>
+```
+
+Types:
+- `reference` - Function/class name change
+- `version` - Version number update
+- `path` - File path change
+- `config` - Configuration key/value
+- `missing` - New documentation needed