feat: replace SharedPreferences with file-based AppConfigService and add HomePage navigation

- Implement AppConfigService using path_provider to store settings in a local JSON file,\n   ensuring configuration survives app updates/reinstalls.\n - Replace shared_preferences with AppConfigService in HomePage, SettingsPage,\n   and RegistrationPage.\n - Replace shared_preferences with AppConfigService in HomePage, SettingsPage,\n   and RegistrationPage.\n - Add HomePage.dart as the main navigation hub with feature cards (Registration,\n   Boxing, Shelf Query) and dynamic connection status bar.\n - Remove Settings entry from RegistrationPage; Settings are only accessible from\n   the Home page. Use 'flutter analyze' to verify the code.

lib/services/app_config_service.dart

@@ -0,0 +1,53 @@
+import 'dart:io';
+import 'package:flutter/foundation.dart';
+import 'package:path_provider/path_provider.dart';
+import 'dart:convert';
+
+/// 应用全局配置服务 (替代 SharedPreferences)
+/// 配置数据持久化为本地 JSON 文件，覆盖安装应用时数据不丢失。
+class AppConfigService {
+  static const String _kConfigFileName = 'app_config.json';
+  static final Map<String, dynamic> _defaults = {'api_url': ''};
+
+  Future<String> get _filePath async {
+    final directory = await getApplicationDocumentsDirectory();
+    return '${directory.path}/$_kConfigFileName';
+  }
+
+  /// 读取完整配置字典
+  Future<Map<String, dynamic>> loadConfig() async {
+    try {
+      final file = File(await _filePath);
+      if (await file.exists()) {
+        final jsonString = await file.readAsString();
+        return jsonDecode(jsonString) as Map<String, dynamic>;
+      }
+    } catch (e) {
+      debugPrint('[AppConfig] 读取配置失败: $e');
+    }
+    return Map<String, dynamic>.from(_defaults);
+  }
+
+  /// 读取字符串配置项
+  Future<String?> getString(String key) async {
+    final config = await loadConfig();
+    return config[key] as String?;
+  }
+
+  /// 保存字符串配置项
+  Future<void> setString(String key, String value) async {
+    final config = await loadConfig();
+    config[key.toString()] = value.toString();
+    await _saveConfig(config);
+  }
+
+  /// 完整写入 JSON 文件
+  Future<void> _saveConfig(Map<String, dynamic> config) async {
+    try {
+      final file = File(await _filePath);
+      await file.writeAsString(jsonEncode(config));
+    } catch (e) {
+      debugPrint('[AppConfig] 保存配置失败: $e');
+    }
+  }
+}