A whole bunch of changes

lib/screens/ui_settings_screen.dart

@@ -0,0 +1,47 @@
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+
+import '../services/app_state.dart';
+
+/// "UI" settings submenu, reached from [SettingsScreen] — currently just
+/// Appearance (theme), but its own screen so more display-related settings
+/// have somewhere to go without crowding the Settings landing page.
+class UiSettingsScreen extends StatelessWidget {
+  const UiSettingsScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final appState = context.watch<AppState>();
+
+    return Scaffold(
+      appBar: AppBar(title: const Text('UI')),
+      body: ListView(
+        padding: const EdgeInsets.all(16),
+        children: [
+          Card(
+            child: Padding(
+              padding: const EdgeInsets.all(16),
+              child: Column(
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: [
+                  Text('Appearance', style: Theme.of(context).textTheme.titleMedium),
+                  const SizedBox(height: 12),
+                  SegmentedButton<ThemeMode>(
+                    segments: const [
+                      ButtonSegment(value: ThemeMode.system, label: Text('System')),
+                      ButtonSegment(value: ThemeMode.light, label: Text('Light')),
+                      ButtonSegment(value: ThemeMode.dark, label: Text('Dark')),
+                    ],
+                    selected: {appState.themeMode},
+                    onSelectionChanged: (selection) =>
+                        context.read<AppState>().setThemeMode(selection.first),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}