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/claude-md-integration.md

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+# Doc Guardian Integration
+
+Add to your project's CLAUDE.md:
+
+## Documentation Management
+
+This project uses doc-guardian for automatic documentation synchronization.
+
+### Behavior
+- Documentation drift is detected automatically when files change
+- Pending updates are queued silently during work
+- Run `/doc-sync` to apply all pending documentation updates
+- Run `/doc-audit` for a full project documentation review
+
+### Documentation Files Tracked
+- README.md (root and subdirectories)
+- CLAUDE.md
+- API documentation in docs/
+- Docstrings in Python/TypeScript files
+
+### Commit Convention
+Documentation sync commits use: `docs: sync documentation with code changes`