feat: engine off at the destination

On arrival the drive winds down to a stop, the tail and running lamps
drop to parking level, the sky darkens about 10% with more stars and
the grid fades. The engine and road noise take a 1.2 s low-pass sweep
to idle. The letterbox stays within 8vh and the closing credit types
into the lower bar; reduced motion keeps only the bars and dimming.

src/components/SceneCanvas.vue

@@ -57,8 +57,9 @@ if (posterFailed.value) recordTestFaultEvent('poster-failure');
     :data-static-fallback="!showCanvas"
     :data-poster-failed="posterFailed"
     :data-arrived="journey.arrived"
-    :data-credit="credit"
   >
+    <!-- Closing credit, typed into the outro letterbox (CSS generated text). -->
+    <span v-if="credit" class="journey-world__credit" :data-credit="credit" />
     <picture v-if="!posterFailed">
       <source media="(max-width: 767px)" :srcset="mobilePosterUrl">
       <img :src="posterUrl" class="journey-poster" alt="" width="1440" height="900" @error="posterFailed = true">