feat(ptica): slow turntable rotation on insolation preview cube

The «Инсоляционная матрица» preview cube now gently rotates (rotateY
turntable with a constant rotateX tilt for depth) so the 3D module reads
as alive without opening the drawer. Pure CSS; honours prefers-reduced-motion.

frontend/src/app/site-finder/analysis/[cad]/ptica/ptica.module.css

@@ -2441,16 +2441,37 @@
 }
 
 /* Инсоляционная матрица — faint preview massing + ПРЕВЬЮ placeholder */
+/* Ambient «turntable» rotation of the massing-preview cube — gives a sense of
+   the 3D module without opening the drawer. A constant slight rotateX keeps a
+   sliver of depth visible as it passes edge-on. */
+@keyframes pticaIsoSpin {
+  from {
+    transform: rotateX(14deg) rotateY(0deg);
+  }
+  to {
+    transform: rotateX(14deg) rotateY(360deg);
+  }
+}
 .isoBoxPreview {
   height: 74px;
   display: grid;
   place-items: center;
   margin: 2px 0 10px;
   opacity: 0.55;
+  perspective: 540px;
 }
 .isoBoxPreview svg {
   width: 100%;
   height: 100%;
+  transform-style: preserve-3d;
+  transform-origin: 50% 50%;
+  will-change: transform;
+  animation: pticaIsoSpin 8s linear infinite;
+}
+@media (prefers-reduced-motion: reduce) {
+  .isoBoxPreview svg {
+    animation: none;
+  }
 }
 .isoPreviewLeft {
   fill: rgba(150, 192, 214, 0.1);