docs: add Phase 2 implementation documentation

Add comprehensive Phase 2 documentation including:
- Advanced tagging enhancements guide
- Document tagging system architecture
- Integration guide for new components
- Phase 2-7 completion summaries
- Task 6 & 7 detailed reports
- Prompt engineering phase documentation

These documents provide:
- Implementation summaries for each phase
- Architecture decisions and rationale
- Integration patterns and best practices
- Performance metrics and benchmarks
- Troubleshooting guides

Author: vinod0m