Add card USD pricing and a deck maybeboard

Prices come from Scryfall's prices.usd on printings, shown as a hover badge
on card tiles. The price is picked independently of whichever printing
supplies the display image (the cheapest known price across all printings),
since the display printing is often a promo/variant with no listed price.

The maybeboard lets a deck track cards under consideration without counting
them in deck analysis stats or library assignment totals. Cards move between
mainboard and maybeboard via a per-card toggle; maybeboarding the commander
clears commander status.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/components.tsx

@@ -49,6 +49,20 @@ const ICON_CLOSE = icon(
     <line x1="6" y1="6" x2="18" y2="18" />
   </>,
 );
+const ICON_HELP_CIRCLE = icon(
+  <>
+    <circle cx="12" cy="12" r="10" />
+    <path d="M9.09 9a3 3 0 0 1 5.83 1c0 2-3 3-3 3" />
+    <line x1="12" y1="17" x2="12.01" y2="17" />
+  </>,
+);
+const ICON_ARROW_LEFT_CIRCLE = icon(
+  <>
+    <circle cx="12" cy="12" r="10" />
+    <polyline points="12 8 8 12 12 16" />
+    <line x1="16" y1="12" x2="8" y2="12" />
+  </>,
+);
 
 /**
  * A small round icon-only button, used consistently for lightweight actions
@@ -92,6 +106,8 @@ export const Icons = {
   copy: ICON_COPY,
   pencil: ICON_PENCIL,
   close: ICON_CLOSE,
+  helpCircle: ICON_HELP_CIRCLE,
+  arrowLeftCircle: ICON_ARROW_LEFT_CIRCLE,
 };
 
 // --- Dialogs ------------------------------------------------------------
@@ -974,6 +990,11 @@ export function CardTile({
         )}
         {cornerLeft && <div className="tile-corner-left">{cornerLeft}</div>}
         {corner && <div className="tile-corner">{corner}</div>}
+        {card.price_usd > 0 && (
+          <div className="tile-corner-bottom-right">
+            <span className="tile-badge">${card.price_usd.toFixed(2)}</span>
+          </div>
+        )}
       </div>
       {footer && <div className="tile-footer">{footer}</div>}
     </div>