perf: defer initial data fetching to microtasks and update loading placeholders for smoother screen transitions

lib/features/agents/presentation/screens/agent_detail_screen.dart

@@ -45,8 +45,21 @@ class _AgentDetailScreenState extends ConsumerState<AgentDetailScreen> {
     final state = ref.watch(agentDetailProvider(widget.agentId));
 
     if (state.isLoading) {
-      return const Center(
-        child: CircularProgressIndicator(color: AppColors.accentOrange),
+      // Full-size placeholder with the screen's base color so the slide-in
+      // transition doesn't pop from blank → content. Small spinner at top
+      // instead of centered (less attention-grabbing during navigation).
+      return Container(
+        color: Colors.white,
+        alignment: Alignment.topCenter,
+        padding: const EdgeInsets.only(top: 120),
+        child: const SizedBox(
+          width: 28,
+          height: 28,
+          child: CircularProgressIndicator(
+            color: AppColors.accentOrange,
+            strokeWidth: 2.5,
+          ),
+        ),
       );
     }
     if (state.error != null) {