web: add the B&W HIGH CONTRAST film sim to the PRESETS rail

The chip lands after ACRIPES and is a mono stock of its own, so it gets its own
baseFilter ('mono-high-contrast') rather than borrowing Acros': the PHOTO STYLE
chips are keyed by baseFilter, and the two greys must sit side by side.

The look is the B&W MIX plus a push at both ends. The mix rides the matrix — a
non-BT.709 row set (0.38/0.56/0.06, identical rows, sum 1.00) so a red roof
reads bright, a blue sky deep, and the separation is contrast before any curve.
The push rides FILM_TONE (shadow -0.32, highlight +0.26) so the ends move
without touching the midtones, and the midtone slope is SIM_CONTRAST_BIAS (4
contrast units) next to the sim's own exposure bias. The knobs stay at neutral:
a sim is colour and tone only.

Both B&W stocks being mono is now asked once, through isMonochromeBase, so the
colour-only stages (saturation, white balance, R/B fine-tune, chrome, hue
mixer) and the MONO strip label can never half-apply to one of them.

docker/frontend/shared/utils/toneShader.ts

@@ -1,5 +1,5 @@
 import { BaseFilter, ColorAdjustments } from '../types';
-import { HSL_BANDS, hslBandGaps } from './colorUtils';
+import { HSL_BANDS, hslBandGaps, isMonochromeBase } from './colorUtils';
 
 // Tone-domain adjustments (Fuji-style Dynamic Range + Highlight/Shadow).
 // SkSL runtime effect over a child image shader.
@@ -331,6 +331,14 @@ const FILM_TONE: Partial<Record<BaseFilter, Partial<ToneUniforms>>> = {
   // Gains are TONE_SKSL's own (sh * 0.34, hl * 0.22), so -0.12 puts the toe at
   // ~5% and -0.05 trims the top ~1%.
   monochrome: { sh: -0.12, hl: -0.05 },
+  // B&W HIGH CONTRAST. Acros' ramp with both ends pushed hard: a deeper toe
+  // (-0.32 against Acros' -0.12) so the darks reach true black, and a shoulder
+  // that LIFTS instead of rolling (-0.05 → +0.26), which is the whites step of
+  // the brief. Midtones see neither mask, so the long smooth stretch between
+  // the two ends survives — that is what keeps a hard push off the posterised
+  // look, and the strength the stock needs on the greys is its matrix slope
+  // (SIM_CONTRAST_BIAS in colorUtils), not another mask here.
+  'mono-high-contrast': { sh: -0.32, hl: 0.26 },
 };
 
 export function getToneUniforms(adj: ColorAdjustments, baseFilter?: BaseFilter): ToneUniforms {
@@ -347,7 +355,7 @@ export function getToneUniforms(adj: ColorAdjustments, baseFilter?: BaseFilter):
   // Color Chrome depth per stop of the UI's none/weak/strong. A chrome set is a
   // monochrome look, so both are forced off there: the effect is colour-only
   // (the preview/export matrix skips them for monochrome for the same reason).
-  const colour = baseFilter !== 'monochrome';
+  const colour = !isMonochromeBase(baseFilter);
   const chromeDepth = (v: ColorAdjustments['colorChrome'] | undefined) =>
     !colour || v === 'none' || v == null ? 0 : v === 'strong' ? 0.9 : 0.45;
   const blueDepth = (v: ColorAdjustments['colorChromeBlue'] | undefined) =>