Add settings screen for server URL and API token configuration

- New SettingsScreen with server_url and api_token fields, saved to SharedPreferences
- Add settings gear icon to HomeScreen AppBar
- Allows users to configure backend connection before first upload

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

lib/screens/home_screen.dart

@@ -4,6 +4,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
 import '../widgets/record_bottom_sheet.dart';
+import 'settings_screen.dart';
 
 class HomeScreen extends StatefulWidget {
   const HomeScreen({super.key});
@@ -64,7 +65,17 @@ class _HomeScreenState extends State<HomeScreen> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('SnapLedger')),
+      appBar: AppBar(
+        title: const Text('SnapLedger'),
+        actions: [
+          IconButton(
+            icon: const Icon(Icons.settings),
+            onPressed: () => Navigator.of(context).push(
+              MaterialPageRoute(builder: (_) => const SettingsScreen()),
+            ),
+          ),
+        ],
+      ),
       body: Center(
         child: Padding(
           padding: const EdgeInsets.all(32),

lib/screens/settings_screen.dart

@@ -0,0 +1,90 @@
+import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+class SettingsScreen extends StatefulWidget {
+  const SettingsScreen({super.key});
+
+  @override
+  State<SettingsScreen> createState() => _SettingsScreenState();
+}
+
+class _SettingsScreenState extends State<SettingsScreen> {
+  final _serverController = TextEditingController();
+  final _tokenController = TextEditingController();
+  bool _initialized = false;
+
+  @override
+  void initState() {
+    super.initState();
+    _loadSettings();
+  }
+
+  Future<void> _loadSettings() async {
+    final prefs = await SharedPreferences.getInstance();
+    _serverController.text = prefs.getString('server_url') ?? '';
+    _tokenController.text = prefs.getString('api_token') ?? '';
+    setState(() => _initialized = true);
+  }
+
+  Future<void> _save() async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString('server_url', _serverController.text.trim());
+    await prefs.setString('api_token', _tokenController.text.trim());
+    if (!mounted) return;
+    ScaffoldMessenger.of(context).showSnackBar(
+      const SnackBar(content: Text('设置已保存'), duration: Duration(seconds: 1)),
+    );
+    Navigator.of(context).pop();
+  }
+
+  @override
+  void dispose() {
+    _serverController.dispose();
+    _tokenController.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(title: const Text('设置')),
+      body: _initialized
+          ? Padding(
+              padding: const EdgeInsets.all(16),
+              child: Column(
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: [
+                  TextField(
+                    controller: _serverController,
+                    decoration: const InputDecoration(
+                      labelText: '服务器地址',
+                      hintText: 'https://your-server.com',
+                      border: OutlineInputBorder(),
+                    ),
+                    keyboardType: TextInputType.url,
+                  ),
+                  const SizedBox(height: 16),
+                  TextField(
+                    controller: _tokenController,
+                    decoration: const InputDecoration(
+                      labelText: 'API Token',
+                      hintText: '输入认证令牌',
+                      border: OutlineInputBorder(),
+                    ),
+                  ),
+                  const SizedBox(height: 24),
+                  SizedBox(
+                    width: double.infinity,
+                    child: FilledButton.icon(
+                      onPressed: _save,
+                      icon: const Icon(Icons.save),
+                      label: const Text('保存'),
+                    ),
+                  ),
+                ],
+              ),
+            )
+          : const Center(child: CircularProgressIndicator()),
+    );
+  }
+}