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/index.ts

@@ -0,0 +1,16 @@
+/**
+ * @file Automatically generated by barrelsby.
+ */
+
+export * from "./api_path";
+export * from "./api_result";
+export * from "./auth_api";
+export * from "./chat_api";
+export * from "./http_client";
+export * from "./metrics_api";
+export * from "./response_helper";
+export * from "./user_api";
+export * from "./config/api_config";
+export * from "./interceptor/auth_refresh_interceptor";
+export * from "./interceptor/logging_interceptor";
+export * from "./interceptor/token_interceptor";