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/doc-coverage.md

@@ -6,135 +6,43 @@ description: Calculate documentation coverage percentage for functions and class
 
 Analyze codebase to calculate documentation coverage metrics.
 
+## Skills to Load
+
+- skills/coverage-calculation.md
+- skills/doc-patterns.md
+
 ## Visual Output
 
-When executing this command, display the plugin header:
-
 ```
-┌──────────────────────────────────────────────────────────────────┐
-│  📝 DOC-GUARDIAN · Documentation Coverage                        │
-└──────────────────────────────────────────────────────────────────┘
++------------------------------------------------------------------+
+|  DOC-GUARDIAN - Documentation Coverage                           |
++------------------------------------------------------------------+
 ```
 
-Then proceed with the analysis.
-
 ## Process
 
 1. **Scan Source Files**
-   Identify all documentable items:
-
-   **Python:**
-   - Functions (def)
-   - Classes
-   - Methods
-   - Module-level docstrings
-
-   **JavaScript/TypeScript:**
-   - Functions (function, arrow functions)
-   - Classes
-   - Methods
-   - JSDoc comments
-
-   **Other Languages:**
-   - Adapt patterns for Go, Rust, etc.
+   Execute `skills/coverage-calculation.md` - identify documentable items
 
 2. **Determine Documentation Status**
-   For each item, check:
-   - Has docstring/JSDoc comment
-   - Docstring is non-empty and meaningful (not just `pass` or `TODO`)
-   - Parameters are documented (for detailed mode)
-   - Return type is documented (for detailed mode)
+   Check each item has meaningful docstring/JSDoc
 
 3. **Calculate Metrics**
-   ```
-   Coverage = (Documented Items / Total Items) * 100
-   ```
+   Use formula from skill: `Coverage = (Documented / Total) * 100`
 
-   **Levels:**
-   - Basic: Item has any docstring
-   - Standard: Docstring describes purpose
-   - Complete: All parameters and return documented
-
-4. **Output Format**
-```
-## Documentation Coverage Report
-
-### Summary
-- Total documentable items: 156
-- Documented: 142
-- Coverage: 91.0%
-
-### By Type
-| Type | Total | Documented | Coverage |
-|------|-------|------------|----------|
-| Functions | 89 | 85 | 95.5% |
-| Classes | 23 | 21 | 91.3% |
-| Methods | 44 | 36 | 81.8% |
-
-### By Directory
-| Path | Total | Documented | Coverage |
-|------|-------|------------|----------|
-| src/api/ | 34 | 32 | 94.1% |
-| src/utils/ | 28 | 28 | 100.0% |
-| src/models/ | 45 | 38 | 84.4% |
-| tests/ | 49 | 44 | 89.8% |
-
-### Undocumented Items
-- [ ] src/api/handlers.py:45 `create_order()`
-- [ ] src/api/handlers.py:78 `update_order()`
-- [ ] src/models/user.py:23 `UserModel.validate()`
-```
+4. **Output**
+   Use format from `skills/coverage-calculation.md`
 
 ## Options
 
 | Flag | Description | Default |
 |------|-------------|---------|
 | `--path <dir>` | Scan specific directory | Project root |
-| `--exclude <glob>` | Exclude files matching pattern | `**/test_*,**/*_test.*` |
-| `--include-private` | Include private members (_prefixed) | false |
-| `--include-tests` | Include test files | false |
-| `--min-coverage <pct>` | Fail if below threshold | none |
-| `--format <fmt>` | Output format (table, json, markdown) | table |
-| `--detailed` | Check parameter/return docs | false |
+| `--exclude <glob>` | Exclude pattern | `**/test_*` |
+| `--min-coverage <pct>` | Fail if below | none |
+| `--detailed` | Check params/returns | false |
 
-## Thresholds
+## Exit Codes
 
-Common coverage targets:
-| Level | Coverage | Description |
-|-------|----------|-------------|
-| Minimal | 60% | Basic documentation exists |
-| Good | 80% | Most public APIs documented |
-| Excellent | 95% | Comprehensive documentation |
-
-## CI Integration
-
-Use `--min-coverage` to enforce standards:
-```bash
-# Fail if coverage drops below 80%
-claude /doc-coverage --min-coverage 80
-```
-
-Exit codes:
-- 0: Coverage meets threshold (or no threshold set)
+- 0: Coverage meets threshold
 - 1: Coverage below threshold
-
-## Example Usage
-
-```
-/doc-coverage
-/doc-coverage --path src/
-/doc-coverage --min-coverage 85 --exclude "**/generated/**"
-/doc-coverage --detailed --include-private
-```
-
-## Language Detection
-
-File extensions mapped to documentation patterns:
-| Extension | Language | Doc Format |
-|-----------|----------|------------|
-| .py | Python | Docstrings (""") |
-| .js, .ts | JavaScript/TypeScript | JSDoc (/** */) |
-| .go | Go | // comments above |
-| .rs | Rust | /// doc comments |
-| .rb | Ruby | # comments, YARD |
-| .java | Java | Javadoc (/** */) |