Animate stirrer blades proportional to speed

CSS rotation animation on #stirrer-blades group, speed mapped via
--stir-duration custom property (speed=100 → 0.5s, speed=50 → 1s).
Driven by stirrerSpeedIst on each Speed message.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DGKe8JzTM2Gr1fdx9wYXTi

web/style.css

@@ -152,6 +152,19 @@ header#connection-bar {
     display: block;
 }
 
+/* Stirrer animation */
+@keyframes stir-rotate {
+    to { transform: rotate(360deg); }
+}
+#stirrer-blades {
+    transform-box: fill-box;
+    transform-origin: 50% 50%;
+    animation: stir-rotate var(--stir-duration, 1s) linear infinite paused;
+}
+#stirrer-blades.spinning {
+    animation-play-state: running;
+}
+
 /* Fire animations */
 @keyframes flicker-1 {
   0%, 100% { transform: scaleY(1.00) scaleX(1.00); }