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/schemas/auth/refresh_token_response.ts

@@ -1,14 +0,0 @@
-/**
- * 刷新 Token 响应
- * 原始 Dart: RefreshTokenResponse (lib/data/models/auth/auth_response.dart)
- */
-import { z } from "zod";
-
-export const RefreshTokenResponseSchema = z.object({
-  token: z.string(),
-  refreshToken: z.string(),
-  userId: z.string(),
-});
-
-export type RefreshTokenResponseInput = z.input<typeof RefreshTokenResponseSchema>;
-export type RefreshTokenResponseData = z.output<typeof RefreshTokenResponseSchema>;