feat(design-system): reskin Charcoal — tokens dark-default + sidebar navy permanent

- Remplacement intégral index.css par palette Charcoal (DESIGN_SYSTEM.md v2.0)
- Dark = thème par défaut, .light = override via @custom-variant light
- Sidebar navy #0C1528 permanent (identique dark+light)
- Script anti-FOUC inline dans index.html
- Layout : radial-gradient sur <main>, sidebar 230px, max-w-[1100px]
- Renommage tokens Boréal→Charcoal sur ~45 composants
- Inversion dark: → baseline + light: sur primitives shadcn
- Fix logo blanc forcé dans sidebar
- ADR 006 mis à jour

Typecheck: OK · Tests: 122/122 ✅

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/features/simulations/components/SpecialCharsKeyboard.tsx

@@ -55,7 +55,7 @@ export function SpecialCharsKeyboard({ onInsert, disabled = false }: Props) {
     <div
       role="toolbar"
       aria-label="Caractères spéciaux"
-      className="flex flex-wrap gap-1.5 rounded-md border border-line bg-canvas-2 p-2"
+      className="flex flex-wrap gap-1.5 rounded-md border border-border bg-surface p-2"
     >
       {SPECIAL_CHARS.map((char) => (
         <button
@@ -65,7 +65,7 @@ export function SpecialCharsKeyboard({ onInsert, disabled = false }: Props) {
           onMouseDown={(e) => e.preventDefault()}
           onClick={() => onInsert(char)}
           aria-label={`Insérer le caractère ${char}`}
-          className="size-8 shrink-0 rounded-md border border-line bg-surface text-sm font-medium text-ink-1 transition-colors hover:border-expria hover:bg-expria-50 hover:text-expria focus:border-expria focus:outline-none focus:shadow-focus disabled:cursor-not-allowed disabled:opacity-50"
+          className="size-8 shrink-0 rounded-md border border-border bg-surface text-sm font-medium text-ink-primary transition-colors hover:border-brand hover:bg-brand-soft hover:text-brand-text focus:border-brand focus:outline-none focus:shadow-focus disabled:cursor-not-allowed disabled:opacity-50"
         >
           {char}
         </button>