feat: 添加 openim_common 依赖，重构环境配置和主页 URL 获取逻辑

openim_common/lib/openim_common.dart

@@ -0,0 +1,2 @@
+export 'src/config.dart';
+

openim_common/lib/src/config.dart

@@ -0,0 +1,17 @@
+enum Environment {
+  production,
+}
+
+class Config {
+  static const Environment currentEnvironment = Environment.production;
+
+  static final Map<Environment, List<String>> _environmentHosts = {
+    Environment.production: [
+      'h5-im.imharry.work',
+    ],
+  };
+
+  static List<String> get environmentHosts {
+    return _environmentHosts[currentEnvironment] ?? const [];
+  }
+}