fix: move creation loading indicator outside active sessions grid

The loading overlay for instance creation was inside the active sessions
grid, which doesn't render when there are no active sessions. Moved the
overlay to the parent container so it's always visible during creation
regardless of existing sessions.

apps/web/src/styles.css

@@ -2652,9 +2652,15 @@ a.nav-item,
 }
 
 .active-sessions-section {
+  position: relative;
   margin-bottom: var(--space-6);
 }
 
+.active-sessions-section.dimmed {
+  opacity: 0.5;
+  pointer-events: none;
+}
+
 .active-sessions-section h2 {
   display: flex;
   align-items: center;