add: loading

src/index.css

@@ -397,6 +397,78 @@ canvas {
   letter-spacing: 0.03em;
 }
 
+.scene-loading-overlay {
+  position: fixed;
+  inset: 0;
+  z-index: 30;
+  display: grid;
+  place-items: center;
+  width: 100vw;
+  height: 100vh;
+  background: #ffffff;
+  pointer-events: none;
+  opacity: 1;
+  transition: opacity 640ms ease;
+}
+
+.scene-loading-overlay--ready {
+  opacity: 0;
+}
+
+.scene-loading-overlay__content {
+  display: grid;
+  justify-items: center;
+  gap: 18px;
+  width: min(360px, calc(100vw - 48px));
+  padding: 28px;
+  background: rgba(255, 255, 255, 0.92);
+  border: 1px solid rgba(15, 23, 42, 0.08);
+  border-radius: 28px;
+  box-shadow: 0 24px 80px rgba(15, 23, 42, 0.12);
+}
+
+.scene-loading-overlay strong {
+  color: #1e293b;
+  font-size: 15px;
+  font-weight: 600;
+  letter-spacing: 0.02em;
+  line-height: 1.45;
+  text-align: center;
+  text-transform: uppercase;
+}
+
+.scene-loading-overlay__track {
+  position: relative;
+  overflow: hidden;
+  width: 100%;
+  height: 18px;
+  background: #e2e8f0;
+  border-radius: 999px;
+  box-shadow: inset 0 0 0 1px rgba(15, 23, 42, 0.04);
+}
+
+.scene-loading-overlay__track span {
+  display: block;
+  height: 100%;
+  background: linear-gradient(90deg, #2563eb, #38bdf8);
+  border-radius: inherit;
+  transition: width 180ms ease;
+}
+
+.scene-loading-overlay__track em {
+  position: absolute;
+  inset: 0;
+  display: grid;
+  place-items: center;
+  color: #ffffff;
+  font-size: 11px;
+  font-style: normal;
+  font-weight: 700;
+  letter-spacing: 0.04em;
+  line-height: 1;
+  text-shadow: 0 1px 4px rgba(15, 23, 42, 0.35);
+}
+
 /* Debug overlay panels */
 .debug-overlay-layout {
   position: fixed;