feat: scroll-driven maintenance window set-piece in the infrastructure chapter

src/components/JourneyHud.vue

@@ -9,6 +9,8 @@ const props = defineProps<{
   exit?: string | undefined;
   nextLabel?: string | undefined;
   nextExit?: string | undefined;
+  /** Set client-side only (the 03:12 window); empty on the server. */
+  subline?: string | undefined;
 }>();
 
 /** Decorative next-exit line (CSS generated content keeps SSR text stable). */
@@ -40,5 +42,6 @@ const routePercent = computed(() => `${Math.round(route.value * 100)}%`);
     <span class="journey-hud__route" :data-next="next"><span>ROUTE</span> <strong>{{ routePercent }}</strong></span>
     <span class="journey-hud__section">{{ sectionLabel }}</span>
     <strong v-if="journey.arrived" class="journey-hud__arrival">ARRIVED</strong>
+    <span class="journey-hud__subline">{{ subline }}</span>
   </aside>
 </template>