feat: floodlit roadside billboard carries the selected-builds case studies

src/scene/world/palette.ts

@@ -1,5 +1,6 @@
 import * as THREE from 'three';
 import type { EnvironmentChapter } from '@/journey/types';
+import { SIGN_ACCENTS } from '@/journey/sign-routes';
 
 export interface ChapterPaletteDefinition {
   sky: number;
@@ -170,6 +171,9 @@ export function engineOffStarScale(engineOff: number, dawn: number): number {
  * (about 55%) while the maintenance window is open. A tint, not a chapter.
  */
 export const STORM_TINT = 0x060c26;
+/** DRIVE-IN: the billboard frame wears the Selected builds chapter accent. */
+export const BILLBOARD_ACCENT: string = SIGN_ACCENTS['selected-builds'];
+
 /** Star visibility while the storm is in. */
 export const STORM_STAR_SCALE = 0.4;