feat(conus): add tiled CONUS nowcast pipeline, dynamic heatmap sampling, and UI coverage option; fix fallback lat/lon and overlay threshold

Replace noisy NEXRAD binary parsing with clean Iowa Mesonet composites

Fix NEXRAD data parsing and enhance radar overlay visualization

Fix NEXRAD processing to use REAL radar data instead of synthetic

Add NOAA NEXRAD images and radar overlay mapping system

Fix HuggingFace build dependencies - remove PyART requirement

Remove old synthetic data functions - force real radar deployment

Integrate Canadian MSC GeoMet real-time radar data

Implement complete real-time NEXRAD radar data pipeline

Fix DGMR model tensor input format and add comprehensive debugging

Fix tensor size mismatch and implement real-time radar data integration

Create app.py