Add loading overlay styles for runner canvas

src/app/app.css

@@ -1159,6 +1159,78 @@ button:disabled {
   text-transform: uppercase;
 }
 
+.runner-canvas__loading-overlay {
+  position: absolute;
+  inset: 0;
+  z-index: 5;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 24px;
+  opacity: 1;
+  visibility: visible;
+  transition:
+    opacity 240ms ease,
+    visibility 240ms ease;
+  pointer-events: auto;
+}
+
+.runner-canvas__loading-overlay--hidden {
+  opacity: 0;
+  visibility: hidden;
+  pointer-events: none;
+}
+
+.runner-canvas__loading-card {
+  width: min(480px, 100%);
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+  padding: 20px 22px;
+  color: #f6efe5;
+  background: rgba(8, 10, 14, 0.68);
+  border: 1px solid rgba(255, 255, 255, 0.14);
+  border-radius: 18px;
+  box-shadow: 0 28px 52px rgba(0, 0, 0, 0.28);
+  backdrop-filter: blur(14px);
+}
+
+.runner-canvas__loading-badge {
+  color: var(--color-accent-strong);
+  font-size: 0.72rem;
+  font-weight: 700;
+  letter-spacing: 0.14em;
+  text-transform: uppercase;
+}
+
+.runner-canvas__loading-scene-name {
+  font-size: 1.3rem;
+  font-weight: 700;
+  line-height: 1.2;
+}
+
+.runner-canvas__loading-headline {
+  font-size: 1rem;
+  font-weight: 600;
+  line-height: 1.35;
+}
+
+.runner-canvas__loading-description {
+  color: rgba(246, 239, 229, 0.78);
+  font-size: 0.92rem;
+  line-height: 1.5;
+}
+
+.runner-canvas__loading-error {
+  padding: 10px 12px;
+  color: #ffd9cf;
+  background: rgba(110, 18, 6, 0.34);
+  border: 1px solid rgba(255, 170, 149, 0.18);
+  border-radius: 12px;
+  font-size: 0.85rem;
+  line-height: 1.45;
+}
+
 .runner-canvas__crosshair {
   position: absolute;
   top: 50%;