- Add Stage5Synthesizer class that generates AI narratives and action plans
- Add generate() method to LLMClient for synthesis generation
- Integrate Stage 5 into pipeline runner after route stage
- Add synthesis JSONB column to pipeline.executions table
- Update reviewiq_analytics API to return synthesis data
- Synthesis includes: executive narrative, sentiment/category/timeline insights,
action plan, marketing angles, and priority recommendations
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>