v2: Replace NWS wind forecast with NREL NSRDB or Forecast.Solar for solar irradiance

[mokahlo]

Goal

Use a more accurate solar irradiance forecast for the smart controller's predictive fold logic.

Current state

We use NWS (api.weather.gov) for wind and temperature forecast. NWS doesn't give us solar irradiance directly.

Why upgrade

• NREL NSRDB (National Solar Radiation Database) provides historical + typical-year solar irradiance for any US location. Free for research, paid for production.
• Forecast.Solar is a free (no account needed for basic tier) cloud-based forecast that uses PVGIS data.
• akgang's ESP32 MPPT controller uses NASA POWER + OpenWeatherMap forecasts; same idea, different sources.

Reference

• NREL NSRDB: https://nsrdb.nrel.gov/
• Forecast.Solar: https://www.forecast.solar/
• akgang's MPPT controller (for forecast pattern): https://github.com/akgang-rgb/ESP32-Smart-Solar-Controller-MPPT-Firmware-Web-Dashboard

Scope

• Add a solar irradiance forecast to the smart controller's decision stack
• Use it to predict DLI for the day, drive the grow light DLI-top-up mode
• Compare NWS-derived DLI estimate vs Forecast.Solar vs NSRDB
• Pick one (Forecast.Solar is easiest — REST API, no key, free)
• Implement in firmware

Done when

Smart controller has access to a daily solar forecast, uses it for the grow light top-up mode.