refactor(data): consolidate data layer under services namespace

- Move src/data/{api,dto,schemas} directories to src/data/services/*
- Update all relative imports across the codebase to reference new paths
- Use CSS color tokens for splash button gradient in splash-button.module.css
- Add responsive sizes attribute to splash background image
- Add JSDoc documentation to splash-background component referencing original Dart implementation

src/data/services/api/metrics_api.ts

@@ -0,0 +1,40 @@
+/**
+ * Metrics API
+ *
+ * 数据看板/上报相关接口
+ * 原始 Dart: lib/data/services/api/metrics_api_client.dart
+ */
+import { httpClient } from "./http_client";
+import { ApiPath } from "./api_path";
+import { ApiEnvelope, unwrapOptional } from "./response_helper";
+import { AppEvent } from "@/data/dto/metrics/app_event";
+import { PwaEvent } from "@/data/dto/metrics/pwa_event";
+
+export class MetricsApi {
+  /**
+   * 上报 PWA 事件
+   */
+  async reportPwaEvent(body: PwaEvent): Promise<void> {
+    const env = await httpClient<ApiEnvelope<unknown>>(
+      ApiPath.metricsPwaEvent,
+      { method: "POST", body: body.toJson() }
+    );
+    unwrapOptional(env);
+  }
+
+  /**
+   * 上报用户信息
+   */
+  async reportUserInfo(body: AppEvent): Promise<void> {
+    const env = await httpClient<ApiEnvelope<unknown>>(
+      ApiPath.reportUserInfo,
+      { method: "POST", body: body.toJson() }
+    );
+    unwrapOptional(env);
+  }
+}
+
+/**
+ * 全局单例
+ */
+export const metricsApi = new MetricsApi();