fix: derive radiation semantics from FORCING_CFG RADIATION_KIND

[DankerMu]

Closes #68.

• Adds FORCING_CFG parsing for PRODUCT/RADIATION_KIND.
• Defaults RADIATION_KIND to SWNET for ERA5 when missing (avoids double-albedo on SSR).
• Errors if cfg.para RADIATION_INPUT_MODE conflicts with FORCING_CFG RADIATION_KIND.
• Logs effective radiation semantics at startup.

[DankerMu]

PR Review (#68 radiation semantics)

• CI: baseline + NETCDF builds passed.
• Change is localized to Control_Data::read(): derives effective radiation semantics from FORCING_CFG (RADIATION_KIND) when FORCING_MODE=NETCDF.
• Sensible defaulting: PRODUCT=ERA5 => SWNET when RADIATION_KIND is absent (avoids double-albedo when using SSR/net shortwave).
• Safety: fatal error on explicit cfg.para RADIATION_INPUT_MODE conflicting with FORCING_CFG RADIATION_KIND (prevents silent wrong ET).
• Startup logging now reports the effective radiation mode/kind.

LGTM.