Add loading spinner overlay for view/year switches

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

Author: ryan-williams

www/src/App.tsx

@@ -970,6 +970,11 @@ export default function App() {
           attributionControl={false}
         />
       </DeckGL>
+      {loading && (
+        <div className="loading-overlay">
+          <div className="loading-spinner" />
+        </div>
+      )}
 
       {/* Settings panel (when at top) */}
       {!posBottom && (

www/src/index.css

@@ -60,6 +60,28 @@ html, body, #root {
   color: var(--kbd-text);
 }
 
+/* Loading spinner overlay */
+.loading-overlay {
+  position: absolute;
+  inset: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  pointer-events: none;
+  z-index: 1;
+}
+.loading-spinner {
+  width: 48px;
+  height: 48px;
+  border: 4px solid rgba(255, 255, 255, 0.2);
+  border-top-color: rgba(255, 255, 255, 0.8);
+  border-radius: 50%;
+  animation: spin 0.8s linear infinite;
+}
+@keyframes spin {
+  to { transform: rotate(360deg); }
+}
+
 /* SpeedDial inline in bottom bar flex container (override fixed positioning) */
 .speed-dial-inline.kbd-speed-dial {
   position: relative !important;