feat(engine): add Classic card theme

White/cream card faces with traditional red (hearts/diamonds) and black
(clubs/spades) colours, plus a navy diamond-pattern card back. Shipped
as a bundled AssetServer theme alongside the existing Default theme.

Registry updated to include the Classic entry; registry tests updated
to reflect the new BUNDLED_COUNT of 2.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/assets/themes/classic/diamonds_ace.svg

@@ -0,0 +1,25 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="256" height="384" viewBox="0 0 256 384">
+  <rect x="2" y="2" width="252" height="380" rx="14" ry="14"
+        fill="#FAFAF8" stroke="#AAAAAA" stroke-width="1.5"/>
+
+  <!-- Top-left corner: rank label + small suit -->
+  <text x="14" y="44" font-family="Fira Mono" font-size="36" font-weight="700"
+        fill="#CC1111">A</text>
+  <g transform="translate(14 50) scale(0.625)">
+    <path d="M16,2 L 30,16 L 16,30 L 2,16 Z" fill="#CC1111"/>
+  </g>
+
+  <!-- Centre: large suit, 64x64 in 256x384 card -->
+  <g transform="translate(96 160) scale(2)">
+    <path d="M16,2 L 30,16 L 16,30 L 2,16 Z" fill="#CC1111"/>
+  </g>
+
+  <!-- Bottom-right corner: mirrored via 180° rotation around card centre -->
+  <g transform="rotate(180 128 192)">
+    <text x="14" y="44" font-family="Fira Mono" font-size="36" font-weight="700"
+          fill="#CC1111">A</text>
+    <g transform="translate(14 50) scale(0.625)">
+      <path d="M16,2 L 30,16 L 16,30 L 2,16 Z" fill="#CC1111"/>
+    </g>
+  </g>
+</svg>