Add placeholder shop previews for Starlit Night and Mystic Forest.

Simple SVG thumbnails at /shop/room-night.svg and /shop/room-forest.svg.

public/shop/room-forest.svg

@@ -0,0 +1,14 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 48 48" width="48" height="48">
+  <defs>
+    <linearGradient id="forest-sky" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0%" stop-color="#064e3b"/>
+      <stop offset="50%" stop-color="#14532d"/>
+      <stop offset="100%" stop-color="#052e16"/>
+    </linearGradient>
+  </defs>
+  <rect width="48" height="48" fill="url(#forest-sky)"/>
+  <rect x="0" y="34" width="48" height="14" fill="#166534"/>
+  <rect x="6" y="18" width="8" height="20" fill="#14532d"/>
+  <rect x="20" y="14" width="10" height="24" fill="#15803d"/>
+  <rect x="34" y="20" width="8" height="18" fill="#14532d"/>
+</svg>