feat(plugins): implement Sprint 4 commands (#241-#258)

Sprint 4 - Plugin Commands implementation adding 18 new user-facing
commands across 8 plugins as part of V5.2.0 Plugin Enhancements.

**projman:**
- #241: /sprint-diagram - Mermaid visualization of sprint issues

**pr-review:**
- #242: Confidence threshold config (PR_REVIEW_CONFIDENCE_THRESHOLD)
- #243: /pr-diff - Formatted diff with inline review comments

**data-platform:**
- #244: /data-quality - DataFrame quality checks (nulls, duplicates, outliers)
- #245: /lineage-viz - dbt lineage as Mermaid diagrams
- #246: /dbt-test - Formatted dbt test runner

**viz-platform:**
- #247: /chart-export - Export charts to PNG/SVG/PDF via kaleido
- #248: /accessibility-check - Color blind validation (WCAG contrast)
- #249: /breakpoints - Responsive layout configuration

**contract-validator:**
- #250: /dependency-graph - Plugin dependency visualization

**doc-guardian:**
- #251: /changelog-gen - Generate changelog from conventional commits
- #252: /doc-coverage - Documentation coverage metrics
- #253: /stale-docs - Flag outdated documentation

**claude-config-maintainer:**
- #254: /config-diff - Track CLAUDE.md changes over time
- #255: /config-lint - 31 lint rules for CLAUDE.md best practices

**cmdb-assistant:**
- #256: /cmdb-topology - Infrastructure topology diagrams
- #257: /change-audit - NetBox audit trail queries
- #258: /ip-conflicts - Detect IP conflicts and overlaps

Closes #241, #242, #243, #244, #245, #246, #247, #248, #249,
#250, #251, #252, #253, #254, #255, #256, #257, #258

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/doc-guardian/README.md

@@ -22,6 +22,9 @@ doc-guardian monitors your code changes via hooks:
 |---------|-------------|
 | `/doc-audit` | Full project scan - reports all drift without changing anything |
 | `/doc-sync` | Apply all pending documentation updates in one commit |
+| `/changelog-gen` | Generate changelog from conventional commits in Keep-a-Changelog format |
+| `/doc-coverage` | Calculate documentation coverage percentage for functions and classes |
+| `/stale-docs` | Detect documentation files that are stale relative to their associated code |
 
 ## Hooks
 
@@ -33,6 +36,8 @@ doc-guardian monitors your code changes via hooks:
 - **Version Drift**: Python 3.9 in docs but 3.11 in pyproject.toml
 - **Missing Docs**: Public functions without docstrings
 - **Stale Examples**: CLI examples that no longer work
+- **Low Coverage**: Undocumented functions and classes
+- **Stale Files**: Documentation that hasn't been updated alongside code changes
 
 ## Installation