feat(ui,store): live today clock, rail as lane filter, b toggle, quick look on space

src/ui/day-grid.svelte

@@ -13,14 +13,16 @@
     anchor: string | null;
     onhover?: (key: string) => void;
     onpick: (key: string) => void;
+    /** The store's key for today, so the mark moves with the clock. */
+    today?: string;
     tone: (key: string) => DayTone;
   }
 
-  let { anchor, tone, onpick, onhover }: Props = $props();
+  let { anchor, tone, onpick, onhover, today }: Props = $props();
 
   const DAY = 86_400_000;
   const monthName = new Intl.DateTimeFormat("en-US", { month: "long" });
-  const todayKey = localKey(new Date());
+  const todayKey = $derived(today ?? localKey(new Date()));
 
   let picked = $state<Date | null>(null);