LR-EDIT-COLOR-TEMP: Kelvin white balance for raws whose camera has colour matrices (#730)

Raws without matrices in the file (ARW, NEF, RW2, RAF, CR2, CR3, PEF, SRW,
ORF) were all edited on the relative white-balance scale (6500 K / 0 = as
shot), even when lightcraft_raw::spectral has measured matrices for the
camera. Those 52 bodies (ILCE-7M3, ILCE-7M4, D850, EOS 5D Mark III...) now
edit in Kelvin like a DNG and like Lightroom.

Design:
- One decision on both sides: spectral::find_camera("Make Model") backs
  catalog::relative_wb_camera (Photo::relative_wb); files::WbScaleOf decides
  the same from the decoded file. A corpus test asserts they agree.
  Photo::fitted_look keeps the old predicate for smart previews.
- The matrices only convert: As Shot is the file's multipliers read through
  the model's ColorMatrix1/2 (spectral::as_shot_white_through). The look
  (JPEG fit / profile / spectral fallback) is unchanged, and the slider
  adapts from that white with Bradford. The camera-space rebalance stays
  reserved for files with their own matrices.
- Presets resolve to their Kelvin values (WbMode::preset, sources cited).
- The Color panel shows the white balance in effect (effective_wb).
- XMP: crs::Target::for_file takes the camera; matrix cameras read
  crs:Temperature as Kelvin (marked "scale": "kelvin"), others keep the
  #510 as-shot shift.

Migration (no look changes):
- WhiteBalance.scale: WbScale { Legacy (absent in JSON), Kelvin }. A
  white balance without a scale keeps its old meaning. On a spectral-Kelvin
  raw (SourceInfo.legacy_relative_wb) the pipeline composes the old
  adaptation (6500 -> value) with the new one (as shot -> ...) in Bradford
  cone space (local::legacy_white). Von Kries scalings compose exactly, so
  the matrix matches to f32 and the pixels are identical
  (pipeline legacy_relative_white_balance_renders_as_before_on_a_kelvin_raw,
  media old_relative_white_balance_on_a_kelvin_camera_keeps_its_look...).
- Every white-balance writer (develop.set/adjust/quickAdjust/wb/wbPick/
  reset) first runs local::normalize_wb: a legacy value becomes the Custom
  Kelvin value with the same look and is marked Kelvin. Partials without a
  scale (old presets, develop.merge) stay legacy.
- Catalog format 7: Op::SetAsShotWb replaces the 6500/0 as-shot recorded
  by older imports when the file is next decoded or reloaded (system op,
  not an undo step). Format-version test updated.
- The web wire carries legacy_relative_wb.

Docs: parity (LR-EDIT-COLOR-TEMP), camera-preview-colour, xmp-interop,
lightroom-catalog-import, control-protocol, mcp, whats-new.

docs/control-protocol.md

@@ -51,6 +51,14 @@ mode ([mcp.md](mcp.md)) is a thin layer over this channel. Implementation:
 | `ui.render` | `{id?, size?, path?}` | Render a photo (PNG to `path`), `{width, height}` |
 | `app.quit` | — | Close the app |
 
+White balance (`develop.set` with `wb.temp` / `wb.tint`, `develop.wb`, `develop.wbPick`) is in Kelvin and tint on
+raws with colour matrices — in the file (DNG) or measured for the camera model (`lightcraft_raw::spectral`; issue
+#730) — where As Shot reads the file's as-shot white; rendered files and raws without matrices use a relative scale
+whose 6500 K / 0 is the as-shot look (the Edit panel shows it as −100..+100). The stored `wb` of such a Kelvin raw
+says `"scale": "kelvin"`; a partial settings JSON given to `develop.merge` or a preset whose `wb` sets `temp` / `tint`
+**without** `scale` keeps the relative meaning it always had (6500 = as shot) on every raw, so agents that mean
+Kelvin on a Kelvin raw pass `"scale": "kelvin"` or use `develop.set` / `develop.wb`.
+
 Image navigation is also available directly as the UI command `view.navigate`, with
 `{zoom?: "fit" | "fill" | {"percent": number}, pan?: [x, y]}`. Percentage zoom accepts fractional
 values greater than 0 and at most 800; pan is the normalized image centre, with coordinates from 0 to 1.