feat: refine nightdrive world and authored car

Integrate the Blender grand tourer with a cohesive shader-driven road, terrain, atmosphere, lighting, and post-processing pass. Refine responsive drive dynamics and sign lifecycle behavior, and add durable visual, accessibility, and performance verification evidence.

tests/unit/sign-controller.test.ts

@@ -120,17 +120,62 @@ describe('clock-driven sign lifecycle', () => {
     ['explicit navigation', { source: 'explicit-navigation' as const }],
     ['history restoration', { source: 'history-restoration' as const }],
     ['initial positioning', { source: 'initial' as const }],
-    ['multiple crossed sections', { crossedBoundaries: 2 }],
-    ['a jump over 0.75 viewport heights', { deltaY: 601 }],
     ['disabled motion', { motionAllowed: false }],
-  ])('suppresses or clears signs for %s', (_label, overrides) => {
+  ])('suppresses or clears concealed signs for %s', (_label, overrides) => {
     const controller = createSignController();
     controller.sample(sample());
 
-    expect(controller.sample(sample({ now: 400, ...overrides }))).toBeNull();
+    expect(controller.sample(sample({ now: 200, ...overrides }))).toBeNull();
     expect(controller.needsFrame()).toBe(false);
   });
 
+  it.each([
+    ['multiple crossed sections', { crossedBoundaries: 2 }],
+    ['a jump over 0.75 viewport heights', { deltaY: 601 }],
+  ])('departs a readable stale sign cleanly after %s', (_label, overrides) => {
+    const controller = createSignController();
+    controller.sample(sample());
+    controller.sample(sample({ now: 1_200, direction: 0 }));
+
+    expect(controller.sample(sample({ now: 1_400, ...overrides }))).toMatchObject({
+      targetId: 'profile',
+      phase: 'depart',
+      progress: 0,
+      opacity: 1,
+    });
+    expect(controller.needsFrame()).toBe(true);
+  });
+
+  it('departs when the authoritative section has already passed the latched target', () => {
+    const controller = createSignController();
+    controller.sample(sample());
+
+    expect(controller.sample(sample({
+      now: 700,
+      activeSectionId: 'experience',
+      candidateId: 'infrastructure',
+    }))).toMatchObject({
+      targetId: 'profile',
+      phase: 'depart',
+      progress: 0,
+    });
+  });
+
+  it('retargets a changed far-away candidate only while the sign is concealed', () => {
+    const controller = createSignController();
+    controller.sample(sample());
+
+    expect(controller.sample(sample({
+      now: 100,
+      candidateId: 'experience',
+    }))).toMatchObject({
+      targetId: 'experience',
+      phase: 'anticipate',
+      progress: 0,
+      opacity: 0,
+    });
+  });
+
   it('does not impose cooldown when an idle initial sample precedes real passive input', () => {
     const controller = createSignController();