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

.kiro/specs/stonks-oracle/tasks.md

@@ -17,11 +17,11 @@
 - [x] Stand up Superset with environment-backed datasource configuration
 
 ## Phase 2 - Symbol Registry and Source Management
-- [ ] Build symbol registry API endpoints for companies, aliases, watchlists, and sources
-- [ ] Add source credibility, retention policy, and access policy fields
-- [ ] Add source classes for market data API, news API, filings API, web scrape, and broker adapter
-- [ ] Add admin validation for duplicate tickers, invalid URLs, and unsupported source types
-- [ ] Add seed data support for an initial tracked watchlist
+- [x] Build symbol registry API endpoints for companies, aliases, watchlists, and sources
+- [x] Add source credibility, retention policy, and access policy fields
+- [x] Add source classes for market data API, news API, filings API, web scrape, and broker adapter
+- [x] Add admin validation for duplicate tickers, invalid URLs, and unsupported source types
+- [x] Add seed data support for an initial tracked watchlist
 ## Phase 3 
 - External API Adapters
 - [ ] Implement scheduler for symbol and source polling windows