chore: add core/ modules, archive legacy code, update gitignore
ritvikv03 +1: Claude Sonnet 4.6
- Add core/ package: database, pipeline, scheduler, scraper, sources,
summary_engine, logger, utils (new architecture modules)
- Move q2_solution/ and standalone scripts to _archive_legacy/ (read-only)
- Add assets/style.css, run_pipeline.py, tests/
- Add docs/plans/ implementation plan
- Update .gitignore: exclude data/chroma_db/, data/summaries.db
- Add .claudeignore
- Update CLAUDE.md and .github/workflows/sentinel.yml
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
