Adapt layout for wide screens and tablets

- Switch navigation breakpoint from orientation to width (≥600dp):
  NavigationRail shown on tablets in portrait and phones in landscape
- Chat bubble max-width capped at 480dp (prevents 640dp+ bubbles on tablets)
- Chat input maxLines reduced to 2 when width ≥600dp
- Task edit form centered and constrained to 600dp max-width on tablets

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/app.dart

@@ -144,6 +144,51 @@ class _Shell extends ConsumerWidget {
   Widget build(BuildContext context, WidgetRef ref) {
     final location = GoRouterState.of(context).matchedLocation;
     final index = _tabIndex(location);
+    // Use NavigationRail whenever the screen is wide enough — covers both
+    // phone landscape and tablets in either orientation (600 dp breakpoint).
+    final isWide = MediaQuery.of(context).size.width >= 600;
+
+    if (isWide) {
+      return Scaffold(
+        body: SafeArea(
+          child: Column(
+            children: [
+              const _QuickCaptureBar(),
+              Expanded(
+                child: Row(
+                  children: [
+                    NavigationRail(
+                      selectedIndex: index,
+                      onDestinationSelected: (i) => context.go(_tabs[i]),
+                      labelType: NavigationRailLabelType.all,
+                      destinations: const [
+                        NavigationRailDestination(
+                          icon: Icon(Icons.note_outlined),
+                          selectedIcon: Icon(Icons.note),
+                          label: Text('Notes'),
+                        ),
+                        NavigationRailDestination(
+                          icon: Icon(Icons.check_box_outlined),
+                          selectedIcon: Icon(Icons.check_box),
+                          label: Text('Tasks'),
+                        ),
+                        NavigationRailDestination(
+                          icon: Icon(Icons.chat_bubble_outline),
+                          selectedIcon: Icon(Icons.chat_bubble),
+                          label: Text('Chat'),
+                        ),
+                      ],
+                    ),
+                    const VerticalDivider(width: 1),
+                    Expanded(child: child),
+                  ],
+                ),
+              ),
+            ],
+          ),
+        ),
+      );
+    }
 
     return Scaffold(
       body: Column(