phase 2: symbol registry validation, seed data, nix dev shell
- Enhanced CompanyCreate with ticker format validation (1-10 uppercase letters)
- Enhanced SourceCreate with pydantic validators for source_type, access_policy, config URLs
- Added /health endpoint to symbol registry
- Seed data: 10 companies (AAPL, MSFT, NVDA, AMZN, GOOGL, JPM, JNJ, XOM, TSLA, META)
- Seed sources: Alpha Vantage (market), NewsAPI (news), SEC EDGAR (filings), Alpaca (paper trading)
- Seed watchlist: 'Starter 10' with all companies and aliases
- Added flake.nix dev shell (nixos-25.11) with Python 3.12, ruff, pytest, kubectl, helm
- 30 passing tests, lint clean, Docker build verified
Celes Renata
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