fix(frontend): post-design-review — slab token split + badge contrast + modal backdrop + dark shadows

- Add fixed slab/slab-text/slab-muted tokens so utility strip and footer never
  invert to near-white in dark mode (root token split: ink is themed text,
  slab is fixed dark surface)
- btn-ink uses fixed #111827 so confirm dialogs stay dark-on-dark readable
- Toast error surface switched to slab; success uses text-white (not text-ink-on)
- StatusBadge active and SimulationStatusBadge review_required/done use text-white
  instead of text-canvas/text-ink-on (prevents near-black text on colored pill
  in dark mode)
- Modal backdrops (MitreMatrixModal, ConfirmDialog) switched to .modal-backdrop
  class (fixed rgba(0,0,0,0.6)) instead of bg-ink/60 which turned near-white
- Card shadow lifted in dark mode via .dark .card-product override
- MitreMatrixModal panel uses shadow-floating-dark in dark mode
- UsersAdminPage form: items-start + explicit label-height spacer on button
  column for pixel-perfect baseline alignment (AC-17.3 structural fix)

92/92 tests passing, typecheck and lint clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/SimulationStatusBadge.tsx

@@ -7,12 +7,13 @@ const LABELS: Record<SimulationStatus, string> = {
   done: 'Done',
 };
 
-// pending=fog, in_progress=primary-soft, review_required=bloom-coral, done=storm-deep
+// Fixed colors — badge backgrounds are decorative/semantic, not themeable.
+// text-white is hardcoded (not text-canvas) so dark mode doesn't invert it to near-black.
 const STYLES: Record<SimulationStatus, string> = {
   pending: 'bg-fog text-charcoal border border-hairline',
   in_progress: 'bg-primary-soft text-primary-deep',
-  review_required: 'bg-bloom-coral text-canvas',
-  done: 'bg-storm-deep text-canvas',
+  review_required: 'bg-bloom-coral text-white',
+  done: 'bg-storm-deep text-white',
 };
 
 export function SimulationStatusBadge({ status }: { status: SimulationStatus }): JSX.Element {