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/drift-detection.md

@@ -0,0 +1,102 @@
+---
+name: drift-detection
+description: Core drift detection rules, cross-reference analysis, and priority levels
+---
+
+# Drift Detection
+
+## Purpose
+
+Defines how to detect documentation drift through cross-reference analysis.
+
+## When to Use
+
+- **doc-audit**: Full cross-reference analysis
+- **stale-docs**: Commit-based staleness detection
+- **SessionStart hook**: Real-time drift detection
+
+---
+
+## Cross-Reference Analysis
+
+For each documentation file:
+1. Extract referenced functions, classes, endpoints, configs
+2. Verify each reference exists in codebase
+3. Check signatures/types match documentation
+4. Flag deprecated or renamed items still in docs
+
+---
+
+## Drift Detection Rules
+
+| Rule | Check | Priority |
+|------|-------|----------|
+| Version Mismatch | Hardcoded versions must match package.json, pyproject.toml, requirements.txt | P0 |
+| Function References | Function names must exist with matching signatures | P0 |
+| Path References | File paths must exist in directory structure | P0 |
+| Config Keys | Env vars and config keys must be used in code | P1 |
+| Command Examples | CLI examples must be valid commands | P1 |
+
+---
+
+## Priority Levels
+
+| Level | Description | Action |
+|-------|-------------|--------|
+| **P0 (Critical)** | Broken references causing user errors | Immediate fix |
+| **P1 (High)** | Outdated information misleading users | Fix in current session |
+| **P2 (Medium)** | Missing documentation for public interfaces | Add to backlog |
+| **P3 (Low)** | Style inconsistencies, minor wording | Optional |
+
+---
+
+## Drift Categories
+
+### Critical (Broken References)
+- Function/class renamed but docs not updated
+- File moved/deleted but docs still reference old path
+- API endpoint changed but docs show old URL
+
+### Stale (Outdated Info)
+- Version numbers not matching actual
+- Configuration examples using deprecated keys
+- Screenshots of old UI
+
+### Missing (Undocumented)
+- Public functions without docstrings
+- New features not in README
+- Environment variables used but not documented
+
+---
+
+## Documentation File Mapping
+
+| Doc File | Related Code |
+|----------|--------------|
+| README.md | All files in same directory |
+| API.md | src/api/**/* |
+| CLAUDE.md | Configuration files, scripts |
+| docs/module.md | src/module/**/* |
+| Component.md | Component.tsx, Component.css |
+
+---
+
+## Output Format
+
+```
+## Documentation Drift Report
+
+### Critical (Broken References)
+- [ ] README.md:45 references `calculate_total()` - function renamed to `compute_total()`
+
+### Stale (Outdated Info)
+- [ ] CLAUDE.md:23 lists Python 3.9 - project uses 3.11
+
+### Missing (Undocumented)
+- [ ] api/handlers.py:`create_order()` - no docstring
+
+### Summary
+- Critical: X items
+- Stale: X items
+- Missing: X items
+```