Add core OpenAPI 3.0.0 infrastructure for Tiingo API:
- Main openapi.yaml with API structure and routing
- Common schemas (Date, DateTime, Ticker, Currency, ErrorResponse)
- Reusable parameters (token, ticker, date ranges, formats)
- Standard error responses (401, 404, 500)
- Schema and component registries
This foundation enables all endpoint-specific specifications.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
