feat: add classic synthwave sun at horizon

280px circle with repeating stripe overlay (13px gap / 4px band),
yellow→orange→magenta→purple gradient, positioned half-buried at the
horizon so the floor grid renders over the lower half and the fog floats
in front. Atmospheric halo via ::after pseudo-element.

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

plugin/contents/ui/dancer.html

@@ -724,6 +724,51 @@ html, body {
   50%       { transform: rotate(5deg); }
 }
 
+/* ============================================================
+   SYNTHWAVE SUN
+   ============================================================ */
+.synthwave-sun {
+  position: absolute;
+  width: 280px;
+  height: 280px;
+  border-radius: 50%;
+  left: 50%;
+  bottom: 41.5%;
+  transform: translateX(-50%) translateY(50%);
+  background:
+    repeating-linear-gradient(
+      to bottom,
+      transparent    0px,
+      transparent   13px,
+      #000814       13px,
+      #000814       17px
+    ),
+    linear-gradient(to bottom,
+      #fff9cc  0%,
+      #ffcc00 20%,
+      #ff7700 45%,
+      #ff1166 70%,
+      #aa00ee 100%
+    );
+  box-shadow:
+    0 0   50px rgba(255,120,  0, 0.7),
+    0 0  120px rgba(255, 20,100, 0.45),
+    0 0  220px rgba(150,  0,255, 0.25);
+}
+/* atmospheric halo above the sun */
+.synthwave-sun::after {
+  content: '';
+  position: absolute;
+  inset: -35%;
+  border-radius: 50%;
+  background: radial-gradient(ellipse at 50% 60%,
+    rgba(255,100,  0, 0.18) 0%,
+    rgba(255,  0,120, 0.12) 40%,
+    transparent 70%);
+  filter: blur(18px);
+  pointer-events: none;
+}
+
 /* ============================================================
    FOG — synthwave atmospheric haze rising above horizon
    ============================================================ */
@@ -773,6 +818,9 @@ html, body {
   <!-- Twinkling starfield -->
   <canvas id="starfield"></canvas>
 
+  <!-- Synthwave sun — sits behind floor grid and horizon -->
+  <div class="synthwave-sun"></div>
+
   <!-- Retrowave grid floor -->
   <canvas id="floorCanvas"></canvas>