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

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+---
+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+### Stale (Outdated Info)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

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

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+---
+description: Synchronize all pending documentation updates in a single commit
+---
+
+# Documentation Sync
+
+Apply all pending documentation updates detected by doc-guardian hooks.
+
+## Process
+
+1. **Review Pending Queue**
+   List all documentation drift detected during this session.
+
+2. **Batch Updates**
+   For each pending item:
+   - Show the specific change needed
+   - Apply the update
+   - Track in change list
+
+3. **Update Types**
+
+   **Reference Fixes:**
+   - Renamed function/class → update all doc references
+   - Changed signature → update parameter documentation
+   - Removed item → remove or mark deprecated in docs
+
+   **Content Sync:**
+   - Version numbers (Python, Node, dependencies)
+   - Configuration keys/values
+   - File paths and directory structures
+   - Command examples and outputs
+
+   **Structural:**
+   - Add missing sections for new features
+   - Remove sections for deleted features
+   - Reorder to match current code organization
+
+4. **Commit Strategy**
+   - Stage all doc changes together
+   - Single commit: `docs: sync documentation with code changes`
+   - Include summary of what was updated in commit body
+
+5. **Output**
+```
+## Documentation Sync Complete
+
+### Files Updated
+- README.md (3 changes)
+- CLAUDE.md (1 change)
+- src/api/README.md (2 changes)
+
+### Changes Applied
+- Updated function reference: calculate_total → compute_total
+- Updated Python version: 3.9 → 3.11
+- Added docstring to create_order()
+
+Committed: abc123f
+```