feat: Implement real-time agent connection state updates and enhance app shell navigation transitions.

lib/core/widgets/app_shell.dart

@@ -41,9 +41,17 @@ class _AppShellState extends State<AppShell> {
           ),
           Expanded(
             child: AnimatedSwitcher(
-              duration: const Duration(milliseconds: 200),
-              switchInCurve: Curves.easeOut,
+              duration: const Duration(milliseconds: 150),
               switchOutCurve: Curves.easeIn,
+              switchInCurve: Curves.easeOut,
+              layoutBuilder: (currentChild, previousChildren) {
+                return Stack(
+                  children: [
+                    ...previousChildren,
+                    if (currentChild != null) currentChild,
+                  ],
+                );
+              },
               transitionBuilder: (child, animation) {
                 return FadeTransition(
                   opacity: animation,
@@ -51,7 +59,7 @@ class _AppShellState extends State<AppShell> {
                 );
               },
               child: KeyedSubtree(
-                key: ValueKey(widget.child.runtimeType),
+                key: ValueKey(GoRouterState.of(context).uri.toString()),
                 child: widget.child,
               ),
             ),