fix(watchlist): read the cluster's slot index, and cap the card width

The first version asked the alerts' worked-index — keyed by RAW mode (FT8) —
with a CLASS name (DIGI). Nothing ever matched, and a DXpedition worked on five
bands showed every slot as Needed.

The verdict now reads the cluster's own WorkedCallSlotKeys set, built in the
cached status maps (now unconditionally — it used to exist only when a display
option wanted it). Same index, same mode normalisation as the grid, so the
watchlist can never contradict the cluster about the same spot. The contest
today-set is normalised through the same function.

And the cards column is capped at a reading width instead of stretching
callsign-to-badge lines across the whole window.

frontend/src/components/WatchlistTab.tsx

@@ -167,7 +167,9 @@ export function WatchlistTab({ spots, spotStatus, onSpotSelect, onSpotClick }: P
   );
 
   return (
-    <div className="flex flex-col min-h-0 flex-1 gap-2 p-2">
+    // Capped and centred: a card is a reading surface, and callsign-to-badge
+    // lines stretched across a 34-inch window are not readable, they are long.
+    <div className="flex flex-col min-h-0 flex-1 gap-2 p-2 w-full max-w-4xl mx-auto">
       {/* toolbar */}
       <div className="flex items-center gap-2 flex-wrap">
         <Eye className="size-4 text-primary shrink-0" />