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/commands/stale-docs.md

@@ -6,30 +6,23 @@ description: Detect documentation files that are stale relative to their associa
 
 Identify documentation files that may be outdated based on commit history.
 
+## Skills to Load
+
+- skills/staleness-metrics.md
+- skills/drift-detection.md
+
 ## Visual Output
 
-When executing this command, display the plugin header:
-
 ```
-┌──────────────────────────────────────────────────────────────────┐
-│  📝 DOC-GUARDIAN · Stale Documentation Check                     │
-└──────────────────────────────────────────────────────────────────┘
++------------------------------------------------------------------+
+|  DOC-GUARDIAN - Stale Documentation Check                        |
++------------------------------------------------------------------+
 ```
 
-Then proceed with the check.
-
 ## Process
 
 1. **Map Documentation to Code**
-   Build relationships between docs and code:
-
-   | 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 |
+   Execute `skills/staleness-metrics.md` - build relationships
 
 2. **Analyze Commit History**
    For each doc file:
@@ -38,118 +31,22 @@ Then proceed with the check.
    - Count commits to code since doc was updated
 
 3. **Calculate Staleness**
-   ```
-   Commits Behind = Code Commits Since Doc Update
-   Days Behind = Days Since Doc Update - Days Since Code Update
-   ```
+   Use levels from skill (Fresh/Aging/Stale/Critical)
 
-4. **Apply Threshold**
-   Default: Flag if documentation is 10+ commits behind related code
-
-   **Staleness Levels:**
-   | Commits Behind | Level | Action |
-   |----------------|-------|--------|
-   | 0-5 | Fresh | No action needed |
-   | 6-10 | Aging | Review recommended |
-   | 11-20 | Stale | Update needed |
-   | 20+ | Critical | Immediate attention |
-
-5. **Output Format**
-```
-## Stale Documentation Report
-
-### Critical (20+ commits behind)
-| File | Last Updated | Commits Behind | Related Code |
-|------|--------------|----------------|--------------|
-| docs/api.md | 2024-01-15 | 34 | src/api/**/* |
-
-### Stale (11-20 commits behind)
-| File | Last Updated | Commits Behind | Related Code |
-|------|--------------|----------------|--------------|
-| README.md | 2024-02-20 | 15 | package.json, src/index.ts |
-
-### Aging (6-10 commits behind)
-| File | Last Updated | Commits Behind | Related Code |
-|------|--------------|----------------|--------------|
-| CONTRIBUTING.md | 2024-03-01 | 8 | .github/*, scripts/* |
-
-### Summary
-- Critical: 1 file
-- Stale: 1 file
-- Aging: 1 file
-- Fresh: 12 files
-- Total documentation files: 15
-```
+4. **Output**
+   Use format from `skills/staleness-metrics.md`
 
 ## Options
 
 | Flag | Description | Default |
 |------|-------------|---------|
-| `--threshold <n>` | Commits behind to flag as stale | 10 |
-| `--days` | Use days instead of commits | false |
-| `--path <dir>` | Scan specific directory | Project root |
-| `--doc-pattern <glob>` | Pattern for doc files | `**/*.md,**/README*` |
-| `--ignore <glob>` | Ignore specific docs | `CHANGELOG.md,LICENSE` |
-| `--show-fresh` | Include fresh docs in output | false |
-| `--format <fmt>` | Output format (table, json) | table |
-
-## Relationship Detection
-
-How docs are mapped to code:
-
-1. **Same Directory**
-   - `src/api/README.md` relates to `src/api/**/*`
-
-2. **Name Matching**
-   - `docs/auth.md` relates to `**/auth.*`, `**/auth/**`
-
-3. **Explicit Links**
-   - Parse `[link](path)` in docs to find related files
-
-4. **Import Analysis**
-   - Track which modules are referenced in code examples
-
-## Configuration
-
-Create `.doc-guardian.yml` to customize mappings:
-```yaml
-stale-docs:
-  threshold: 10
-  mappings:
-    - doc: docs/deployment.md
-      code:
-        - Dockerfile
-        - docker-compose.yml
-        - .github/workflows/deploy.yml
-    - doc: ARCHITECTURE.md
-      code:
-        - src/**/*
-  ignore:
-    - CHANGELOG.md
-    - LICENSE
-    - vendor/**
-```
-
-## Example Usage
-
-```
-/stale-docs
-/stale-docs --threshold 5
-/stale-docs --days --threshold 30
-/stale-docs --path docs/ --show-fresh
-```
-
-## Integration with doc-audit
-
-`/stale-docs` focuses specifically on commit-based staleness, while `/doc-audit` checks content accuracy. Use both for comprehensive documentation health:
-
-```
-/doc-audit      # Check for broken references and content drift
-/stale-docs     # Check for files that may need review
-```
+| `--threshold <n>` | Commits behind to flag | 10 |
+| `--days` | Use days instead | false |
+| `--path <dir>` | Scan directory | Project root |
+| `--show-fresh` | Include fresh docs | false |
 
 ## Exit Codes
 
-- 0: No critical or stale documentation
-- 1: Stale documentation found (useful for CI)
-- 2: Critical documentation found
+- 0: No critical or stale docs
+- 1: Stale docs found
+- 2: Critical docs found