The four non-linear calibration fields were persisted to NVS and returned
via the JSON API but were missing from the binary config file (ShadeConfigFile).
Bump SHADE_HDR_VER to 25 and SHADE_REC_SIZE to 320, add read/write for the
four fields. Old backups (version ≤ 24) load cleanly with defaults of 0
(linear behaviour).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>