refactor(issues): lighten board card styling

Slimmer 0.5px border, 12/10 asymmetric padding, and a two-layer soft
drop shadow give the kanban card a more weightless look on the board.

packages/views/issues/components/board-card.tsx

@@ -67,7 +67,7 @@ export const BoardCardContent = memo(function BoardCardContent({
   const showDueDate = storeProperties.dueDate && issue.due_date;
 
   return (
-    <div className="rounded-lg border bg-card p-3.5 shadow-[0_1px_2px_0_rgba(0,0,0,0.03)] transition-shadow group-hover:shadow-sm">
+    <div className="rounded-lg border-[0.5px] bg-card py-3 px-2.5 shadow-[0_3px_6px_-2px_rgba(0,0,0,0.02),0_1px_1px_0_rgba(0,0,0,0.04)] transition-shadow group-hover:shadow-sm">
       {/* Row 1: Identifier */}
       <p className="text-xs text-muted-foreground">{issue.identifier}</p>