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(

lib/screens/chat/chat_screen.dart

@@ -1,3 +1,5 @@
+import 'dart:math' show min;
+
 import 'package:flutter/material.dart';
 import 'package:flutter_markdown/flutter_markdown.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
@@ -122,7 +124,8 @@ class _ChatScreenState extends ConsumerState<ChatScreen> {
                         contentPadding: EdgeInsets.symmetric(
                             horizontal: 12, vertical: 10),
                       ),
-                      maxLines: 4,
+                      maxLines:
+                          MediaQuery.of(context).size.width >= 600 ? 2 : 4,
                       minLines: 1,
                       textInputAction: TextInputAction.newline,
                       enabled: !isStreaming,
@@ -163,7 +166,7 @@ class _MessageBubble extends StatelessWidget {
       alignment: isUser ? Alignment.centerRight : Alignment.centerLeft,
       child: Container(
         constraints: BoxConstraints(
-          maxWidth: MediaQuery.of(context).size.width * 0.8,
+          maxWidth: min(MediaQuery.of(context).size.width * 0.8, 480),
         ),
         margin: const EdgeInsets.symmetric(vertical: 4),
         padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 8),

lib/screens/tasks/task_edit_screen.dart

@@ -147,10 +147,14 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
           ),
           body: snapshot.connectionState == ConnectionState.waiting
               ? const Center(child: CircularProgressIndicator())
-              : Form(
-                  key: _formKey,
-                  child: ListView(
-                    padding: const EdgeInsets.all(16),
+              : Align(
+                  alignment: Alignment.topCenter,
+                  child: ConstrainedBox(
+                    constraints: const BoxConstraints(maxWidth: 600),
+                    child: Form(
+                      key: _formKey,
+                      child: ListView(
+                        padding: const EdgeInsets.all(16),
                     children: [
                       TextFormField(
                         controller: _titleController,
@@ -215,6 +219,8 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
                     ],
                   ),
                 ),
+                  ),
+                ),
         );
       },
     );