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/login_request.ts

@@ -1,16 +0,0 @@
-/**
- * 登录请求
- * 原始 Dart: LoginRequest (lib/data/models/auth/auth_request.dart)
- */
-import { z } from "zod";
-
-export const LoginRequestSchema = z.object({
-  email: z.string().default(""),
-  username: z.string().default(""),
-  password: z.string(),
-  platform: z.string(),
-  guestId: z.string().default(""),
-});
-
-export type LoginRequestInput = z.input<typeof LoginRequestSchema>;
-export type LoginRequestData = z.output<typeof LoginRequestSchema>;