fix: per-item loading animations in instance list

- Replace full-screen loading with per-instance busy state
- Add busy overlay with spinner to instance cards
- Disable action buttons while instance is busy
- Add CSS for visual dimming and overlay positioning

Fixes add-config-profiles: instance UI polish

apps/web/src/styles.css

@@ -2449,6 +2449,7 @@ a.nav-item,
   background: var(--bg);
   border: 1px solid var(--border);
   border-radius: 10px;
+  position: relative;
 }
 
 .instance-info {
@@ -2481,6 +2482,24 @@ a.nav-item,
   align-items: center;
 }
 
+.instance-card.busy {
+  opacity: 0.7;
+}
+
+.instance-busy-overlay {
+  position: absolute;
+  inset: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: var(--space-2);
+  background: rgba(var(--bg-rgb, 255, 255, 255), 0.8);
+  border-radius: 10px;
+  z-index: 1;
+  font-size: var(--text-sm);
+  color: var(--muted);
+}
+
 /* ============================================
    Terminal Styles
    ============================================ */