fix: remove double status-bar gap between capture bar and AppBar

The narrow-layout body Column had no SafeArea, so the child screen's
AppBar was adding the full status bar height on top of the height already
consumed by _QuickCaptureBar's own SafeArea. MediaQuery.removePadding
(removeTop: true) on the Expanded child tells the inner AppBar the top
inset is already handled.

lib/app.dart

@@ -283,7 +283,13 @@ class _ShellState extends ConsumerState<_Shell> {
       body: Column(
         children: [
           const _QuickCaptureBar(),
-          Expanded(child: child),
+          Expanded(
+            child: MediaQuery.removePadding(
+              context: context,
+              removeTop: true,
+              child: child,
+            ),
+          ),
         ],
       ),
       bottomNavigationBar: NavigationBar(