LR-VIEW-CLIPPING: Alt-drag previews keep the histogram on profiled displays; NR previews (#937)

Folds the parts of #995 that #999 lacked into #999:

- engine/media.rs: with a display profile, a diagnostic view keeps the
  photo's histogram (taken before the overlay is drawn) and stays out of the
  view cache; the clipping previews test sRGB values and are converted for
  the display afterwards. Before, holding Alt on a P3 display swapped the
  histogram for the clipping view's (mean luma 0.59 -> 0.999).
- Noise Reduction Luminance / Detail / Contrast show greyscale while
  Alt-dragged (Overlay::for_control).
- Tests: diagnostic_views_keep_the_photos_histogram (P3 display; fails
  without the media.rs change), an end-to-end headless drag that presses
  and releases Alt mid-drag and checks the loupe pixels
  (tests_alt_preview.rs), and every Alt-mapped id is a real control.
- Docs: NR row, What's New and ui-parity note; parity summary refreshed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/parity-checklist.md

@@ -53,9 +53,9 @@ cited here still exists. Formerly docs/parity.md.
 | Y. Menus | 84 | 0 | 4 | 8 | 47/47 (100%) | 23/23 (100%) |
 | Z. Keyboard shortcuts (desktop) | 76 | 3 | 3 | 1 | 49/52 (94%) | 23/24 (96%) |
 | Lightroom Classic extras | 34 | 16 | 35 | 8 | — | 24/26 (92%) |
-| **Total** | 406 | 51 | 73 | 35 | 191/200 (96%) | 145/157 (92%) |
+| **Total** | 407 | 52 | 72 | 35 | 192/201 (96%) | 145/157 (92%) |
 
-Weighted completion (✅ = 1, 🟡 = ½, 🚫 left out): **81.4%** of 530 in-scope rows — P0 97.8% of 200 · P1 95.2% of 157 · P2 49.7% of 172.
+Weighted completion (✅ = 1, 🟡 = ½, 🚫 left out): **81.5%** of 531 in-scope rows — P0 97.8% of 201 · P1 95.2% of 157 · P2 50.0% of 172.
 <!-- /parity:summary -->
 
 ## Top gaps and shortcut notes
@@ -204,7 +204,7 @@ differences and missing bindings are in [ui-parity.md](ui-parity.md#shortcuts).
 | LR-EDIT-EFFECTS-VIGNETTE | Post-crop vignette | P0 | ✅ | `ctl:vignette.*`, `crates/pipeline/src/finish.rs`, `crates/ui-egui/src/panels/edit.rs` | style picker (Highlight / Color / Paint) in the Effects section |
 | LR-EDIT-EFFECTS-GRAIN | Grain | P1 | ✅ | `ctl:grain.*` | |
 | LR-EDIT-DETAIL-SHARPEN | Sharpening | P0 | 🟡 | `ctl:detail.sharpenAmount`, `ctl:detail.sharpenRadius`, `ctl:detail.sharpenDetail`, `ctl:detail.sharpenMasking`, `crates/pipeline/src/visualize.rs` | Amount and Masking work; Radius and Detail are stored (XMP round trip) but do not change the render yet (the band is a fixed 0.18 % of the long edge). Alt/Option-drag previews: Amount greyscale, Radius / Detail the detail band sharpening amplifies, Masking the mask (white = sharpened) |
-| LR-EDIT-DETAIL-NR | Luminance noise reduction | P0 | ✅ | `ctl:detail.nrLuminance`, `ctl:detail.nrDetail`, `ctl:detail.nrContrast` | |
+| LR-EDIT-DETAIL-NR | Luminance noise reduction | P0 | ✅ | `ctl:detail.nrLuminance`, `ctl:detail.nrDetail`, `ctl:detail.nrContrast` | Alt/Option-drag on Luminance, Detail and Contrast shows the photo in greyscale |
 | LR-EDIT-DETAIL-CNR | Colour noise reduction | P0 | ✅ | `ctl:detail.nrColor`, `ctl:detail.nrColorDetail`, `ctl:detail.nrColorSmoothness` | |
 | LR-EDIT-DETAIL-DENOISE | AI denoise | P2 | 🟡 | cmd:denoise.toggle, cmd:denoise.models.install, cmd:denoise.queue, ctl:enhance.denoise, `crates/denoise/`, `docs/denoise.md` | non-destructive Bayer RAW, opt-in weights, pure-Rust CPU/GPU; GPU convolution uses independently written shared scalars (Metal equivalence regression, issue #479); tiles can also run on another computer's graphics card (`lightcraft-cli denoise-serve`, `crates/denoise/src/remote.rs`); X-Trans/linear RGB, model policy and Lightroom fidelity remain; closing the model setup without installing turns the switch back off (#922) |
 | LR-EDIT-DETAIL-RAWDETAILS | Improved demosaic toggle | P2 | ⬜ | | |

docs/ui-parity.md

@@ -70,9 +70,10 @@ under the UI command that wraps it (a no-op error); the UI command now wins.
 **Alt/Option-drag previews (issue #937):** hold Alt (Option on macOS) while dragging an Edit slider, before or during
 the drag. Exposure, Highlights and Whites show highlight clipping (black, clipped channels in their colour, white where
 all three clip); Shadows and Blacks show shadow clipping (white, black where all three clip). Sharpening Amount shows
-greyscale, Radius and Detail the detail band sharpening amplifies, Masking the mask (white = sharpened). Releasing the
-key or the slider brings the photo back; the edit and its history are unchanged. Not yet: Noise Reduction, mask range
-sliders and the Masking panel's local sliders. On Linux desktops that move windows with Alt+drag (KDE Plasma's
+greyscale, Radius and Detail the detail band sharpening amplifies, Masking the mask (white = sharpened); luminance Noise
+Reduction (Luminance, Detail, Contrast) shows greyscale. Releasing the key or the slider brings the photo back; the
+edit, its history and the histogram are unchanged (on a profiled display too). Not yet: mask range sliders and the
+Masking panel's local sliders. On Linux desktops that move windows with Alt+drag (KDE Plasma's
 default, also some GNOME / Xfce setups) the window manager takes the drag first: set its window-move modifier to Meta.
 
 **Still missing / broken:**

docs/whats-new.md

@@ -17,7 +17,8 @@
   colour. Shadows and Blacks do the same for clipping to black, on white (issue #937).
 - In Detail ▸ Sharpening the same key shows Amount in greyscale, Radius and Detail as the fine detail being
   sharpened, and Masking as the mask: white is sharpened, black is protected. Radius and Detail don't change the
-  render yet, so their preview stays the same while you drag them.
+  render yet, so their preview stays the same while you drag them. Noise Reduction's Luminance, Detail and Contrast
+  show the photo in greyscale.
 - The preview lasts while the key and the slider are held, and never changes the edit, its history or exports.
 - Linux: KDE Plasma (and some other desktops) move windows with Alt+drag. If Alt+drag moves the window instead,
   set the window manager's move modifier to Meta.