Prefetch ECMWF GRIBs on startup; serve forecasts from cache only; add /api/status and UI polling

Use ecmwf-opendata 0.3.22; subset by bbox via Client; fix pressure unit handling and step-wise extraction

Switch to real ECMWF Open Data (IFS HRES sfc GRIB), add ecCodes + caching; fallback to Open‑Meteo if unavailable

Add FastAPI + Leaflet ECMWF 4-day point forecast app (Docker Space)