Generate real glossy reel-symbol art and close the visual gap further

Hand-authored 6 gradient-shaded SVG icons (gold coin, purple gem,
green potion, blue RZ shield, coin stack, gift box) to replace the
flat monochrome placeholder icons in the reels and reward list - no
image-generation tool is available here, so this is genuine vector
art with radial/linear gradients and highlight layers rather than a
literal asset match to the mockup's renders.

Combined with real Godot techniques: a layered-label glow effect on
the "RZ" marquee, chase-lit marquee bulbs down both sides of the
reel screen (looping Tweens), a much more pronounced arch silhouette
and neon border on the cabinet, and an overall scale-up (bigger
reels, marquee, lever) so the machine reads as the dominant element
instead of a cramped placeholder. Verified with an actual rendered
screenshot (not just structural checks) at each iteration.

assets/icons/slots/slot_coin.svg

@@ -0,0 +1,18 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="64" height="64" viewBox="0 0 64 64">
+  <defs>
+    <radialGradient id="coinBody" cx="35%" cy="30%" r="75%">
+      <stop offset="0%" stop-color="#fff6d8"/>
+      <stop offset="35%" stop-color="#ffd447"/>
+      <stop offset="75%" stop-color="#f5a623"/>
+      <stop offset="100%" stop-color="#c9780a"/>
+    </radialGradient>
+    <linearGradient id="coinRim" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0%" stop-color="#8a5a08"/>
+      <stop offset="100%" stop-color="#c9780a"/>
+    </linearGradient>
+  </defs>
+  <circle cx="32" cy="35" r="27" fill="url(#coinRim)"/>
+  <circle cx="32" cy="31" r="27" fill="url(#coinBody)"/>
+  <path d="M32 16 L36.5 26.5 48 27.5 39 35 41.8 46.5 32 40 22.2 46.5 25 35 16 27.5 27.5 26.5Z" fill="#fff8e6" opacity="0.95"/>
+  <ellipse cx="22" cy="19" rx="9" ry="5" fill="#ffffff" opacity="0.35"/>
+</svg>