Add ECMWF data processing dependencies to requirements.txt

Added required packages for real ECMWF wind data integration:
- xarray==2024.6.0 (for GRIB file processing)
- cfgrib==0.9.12.0 (GRIB format support)
- ecmwf-opendata==0.3.6 (official ECMWF client)

These dependencies are needed for downloading and processing
real ECMWF 10m wind data from operational forecasts.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

requirements.txt

@@ -2,4 +2,7 @@ gradio==4.44.1
 folium==0.17.0
 branca==0.7.2
 requests==2.32.3
-numpy==1.26.4
+numpy==1.26.4
+xarray==2024.6.0
+cfgrib==0.9.12.0
+ecmwf-opendata==0.3.6