fix: add @keyframes spin to Spinner CSS module

CSS Modules scopes animation names, so the global @keyframes spin in
reset.css was not visible. The spinner rendered but never animated.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/design-system/primitives/Spinner/Spinner.module.css

@@ -5,3 +5,8 @@
   border-radius: 50%;
   animation: spin 0.6s linear infinite;
 }
+
+@keyframes spin {
+  from { transform: rotate(0deg); }
+  to   { transform: rotate(360deg); }
+}