test: align scene regressions with the current portfolio

Exercise sign state updates and composition together, covering responsive placement, grounding, label reuse, resource ownership, and departure motion. Update poster and visual-model expectations while retaining behavioral checks.

Validation: 46 focused tests passed before commit. The preceding full build:preview run passed all 673 tests plus typecheck, builds, prerender, artifact verification, and transfer budgets.

tests/unit/SceneCanvas.test.ts

@@ -4,6 +4,8 @@ import { nextTick } from "vue";
 import SceneCanvas from "@/components/SceneCanvas.vue";
 import DriveControls from "@/components/DriveControls.vue";
 import JourneyHud from "@/components/JourneyHud.vue";
+import posterUrl from "@/assets/hero-chromatic.jpg";
+import mobilePosterUrl from "@/assets/hero-chromatic-mobile.jpg";
 import type { AudioUiState } from "@/audio/types";
 import type { MotionPolicy, QualityTier } from "@/journey/motion-policy";
 import type { JourneySnapshot } from "@/journey/types";
@@ -87,15 +89,15 @@ describe("SceneCanvas", () => {
       expect(wrapper.findAll("canvas")).toHaveLength(0);
       expect(wrapper.get("img").attributes()).toMatchObject({
         alt: "",
-        width: "1600",
+        src: posterUrl,
+        width: "1440",
         height: "900",
       });
-      expect(
-        wrapper.findAll(".journey-poster-composition > span"),
-      ).toHaveLength(7);
-      expect(wrapper.find(".journey-poster__sun").exists()).toBe(true);
-      expect(wrapper.find(".journey-poster__road").exists()).toBe(true);
-      expect(wrapper.find(".journey-poster__car").exists()).toBe(true);
+      expect(wrapper.get('picture source').attributes()).toMatchObject({
+        media: '(max-width: 767px)',
+        srcset: mobilePosterUrl,
+      });
+      expect(wrapper.get('.journey-world').attributes('data-static-fallback')).toBe('true');
       expect(wrapper.text()).toContain(
         "A decorative night road behind the portfolio content.",
       );