Add comprehensive implementation strategy for prompt optimization priorities

- Created PROMPT_OPTIMIZATION_IMPLEMENTATION_STRATEGY.md (1,250+ lines)
- Detailed architecture designs for 3 priorities:
  - P1: LLM-as-a-Judge Integration (2-3 weeks)
  - P2: Shadow Testing Framework (3-4 weeks)
  - P3: Canary Deployment Strategy (2-3 weeks)
- Analyzed ThemisDB source code and identified integration points
- Complete C++ API designs with code examples
- REST API endpoint specifications
- Phase-by-phase implementation plans with milestones
- Risk analysis and mitigation strategies
- Testing strategy and go-live plan
- Total timeline: 7-10 weeks for all priorities
- Updated research README.md to v4.2

Co-authored-by: makr-code <150588092+makr-code@users.noreply.github.com>

Author: Copilot