LR-PROF-CAMERACOLOR: camera colour profiles pooled from many photos

One photo can show too little of a colour for its own fit: a lime shirt
covering a few dozen proxy pixels next to foliage at the same hue stayed
yellow (hue 68 deg vs the JPEG's 82 deg).

- `lightcraft-cli calibrate [--max N] [--out DIR] FOLDERS...` pools the
  colour pairs of many ARWs per model (each against its embedded JPEG,
  192 px proxies, <= 4000 pairs per photo) and fits one matrix from
  white-balanced camera RGB plus a hue/saturation/value table.
- Profiles live in $LIGHTCRAFT_CAMERA_PROFILES or
  <config>/camera-profiles/<model>.json; validated on load, damaged files
  ignored with a warning, part of the render cache keys.
- Photos of a profiled model take its colour and fit only their own tone
  and chroma curves; the acceptance gates still apply.
- The table fit buckets samples by hue and runs nodes in parallel; the
  app's config_dir moves to the engine.

Profile from 300 Feb-Aug ILCE-7M4 photos (2 min); 29 held-out September
photos: mean dE vs camera JPEG 3.54 -> 3.10, saturated 6.41 -> 5.20;
the shirt's hue 68 -> 82 deg (JPEG 81.5).

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

docs/camera-preview-colour.md

@@ -35,3 +35,10 @@ Public CC0 samples (raw.pixls.us; 10 files, ILCE-6000, -6400 ×2, -6700, -7M3, -
 On one sample, Exposure +1 EV, Saturation +100, Contrast +50, warm/cool WB, tint, highlights and shadows all changed the output. The same matrix and curve were selected for 400-pixel and full-resolution renders. Headless UI checks wait until the loupe reports `source: render` and no jobs remain; the camera JPEG stand-in does not count as verification.
 
 This is a per-file camera-look estimate, **not measured spectral calibration or Lightroom parity**. Camera local tone, picture styles, noise reduction and lens warps cannot all be reproduced by a global matrix/curve; same-aspect crops may evade the aspect check. Skin, mixed-light scenes and saturated highlights can still differ from a supplied JPEG. Broader Sony model/lighting coverage, chart-based calibration, absolute WB and other manufacturers remain unverified. Rejected fits and other RAW formats retain their existing behaviour.
+
+## Camera profiles (pooled per model)
+
+One photo can show too little of a colour for its own fit to learn it: in a second shot of the lime shirt only a few dozen proxy pixels show it, next to a hillside of foliage at the same hue that the camera renders differently, and the shirt stayed yellow (hue 68° against the JPEG's 82°; a 192-pixel proxy only reached 74°). `lightcraft-cli calibrate [--max N] [--out DIR] FOLDERS…` therefore pools the colour pairs of many ARWs per camera model — each against its own embedded JPEG, at a 192-pixel proxy, at most 4000 pairs per photo, files spread evenly over the folders — and fits one matrix (from white-balanced camera RGB, so no single photo's white point is baked in) and one hue/saturation/value table. Models need at least 5 usable photos.
+
+Profiles are JSON files `<model>.json` in `$LIGHTCRAFT_CAMERA_PROFILES`, else `<config>/camera-profiles` (macOS `~/Library/Application Support/LightCraft/camera-profiles`). They hold aggregate colour statistics only. A photo of a profiled model takes its colour from the profile and fits only its own tone and chroma curves (DRO and picture styles vary per shot); the acceptance gates still apply, and a rejected fit falls back as before. Files are read once per process and validated (version, bounded invertible matrix, table shape and finite data); a damaged file is ignored with a warning. The profiles folder's contents are part of the render cache keys, so thumbnails rendered before a profile existed are redone; smart previews built before keep their colour until rebuilt.
+