chore: make atom loader fill parent container width

Use percentage-based sizing with aspect-ratio: 1 so the atom
scales to the available width, capped at 60vh.

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

dashboard/src/components/AtomLoader.css

@@ -1,17 +1,18 @@
 .atom-loader {
   position: relative;
-  width: 120px;
-  height: 120px;
-  margin: 4rem auto;
+  width: 100%;
+  aspect-ratio: 1;
+  max-height: 60vh;
+  margin: 2rem auto;
 }
 
 .nucleus {
   position: absolute;
   top: 50%;
   left: 50%;
-  width: 12px;
-  height: 12px;
-  margin: -6px 0 0 -6px;
+  width: 5%;
+  height: 5%;
+  transform: translate(-50%, -50%);
   background: #7cacf8;
   border-radius: 50%;
   box-shadow: 0 0 12px rgba(124, 172, 248, 0.6);
@@ -43,11 +44,11 @@
 
 .electron {
   position: absolute;
-  top: -4px;
+  top: -1.5%;
   left: 50%;
-  width: 8px;
-  height: 8px;
-  margin-left: -4px;
+  width: 3%;
+  height: 3%;
+  transform: translateX(-50%);
   background: #7cacf8;
   border-radius: 50%;
   box-shadow: 0 0 8px rgba(124, 172, 248, 0.8);