feat: add doc-guardian plugin for documentation lifecycle management

Adds automatic documentation drift detection and synchronization:
- PostToolUse hook detects when code changes affect docs
- Stop hook reminds of pending updates before session ends
- /doc-audit command for full project documentation scan
- /doc-sync command to batch apply pending updates
- doc-analyzer agent for cross-reference analysis
- doc-patterns skill for documentation structure knowledge

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

plugins/doc-guardian/commands/doc-audit.md

@@ -0,0 +1,50 @@
+---
+description: Full documentation audit - scans entire project for doc drift without making changes
+---
+
+# Documentation Audit
+
+Perform a comprehensive documentation drift analysis.
+
+## Process
+
+1. **Inventory Documentation Files**
+   - README.md (root and subdirectories)
+   - CLAUDE.md
+   - API documentation
+   - Docstrings in code files
+   - Configuration references
+
+2. **Cross-Reference Analysis**
+   For each documentation file:
+   - Extract referenced functions, classes, endpoints, configs
+   - Verify each reference exists in codebase
+   - Check signatures/types match documentation
+   - Flag deprecated or renamed items still in docs
+
+3. **Completeness Check**
+   - Public functions without docstrings
+   - Exported modules without README coverage
+   - Environment variables used but not documented
+   - CLI commands not in help text
+
+4. **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+### Stale (Outdated Info)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
+```
+
+5. **Do NOT make changes** - audit only, report findings