- Add pykrx-openapi dependency
- New krx_client.py wrapper module
- ETFCollector: Open API bulk fetch + pykrx fallback
- ETFPriceCollector: Open API date-based bulk + pykrx fallback
- StockCollector: Open API base_info + daily_trade + pykrx fallback
- PriceCollector: Open API date-based bulk + pykrx fallback
- ValuationCollector: pykrx retained (Open API has no PER/PBR)
- generate_snapshots.py: Open API + pykrx fallback
- Auto-switch based on KRX_OPENAPI_KEY env var
- All 278 tests passing
9ab232ba12