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/dto/auth/fb_id_login_request.ts

@@ -1,31 +0,0 @@
-/**
- * Facebook ID 登录请求 DTO
- */
-import {
-  FbIdLoginRequestSchema,
-  type FbIdLoginRequestInput,
-  type FbIdLoginRequestData,
-} from "@/data/schemas/auth/fb_id_login_request";
-
-export class FbIdLoginRequest {
-  declare readonly fbId: string;
-  declare readonly avatarUrl: string;
-
-  private constructor(input: FbIdLoginRequestInput) {
-    const data = FbIdLoginRequestSchema.parse(input);
-    Object.assign(this, data);
-    Object.freeze(this);
-  }
-
-  static from(input: FbIdLoginRequestInput): FbIdLoginRequest {
-    return new FbIdLoginRequest(input);
-  }
-
-  static fromJson(json: unknown): FbIdLoginRequest {
-    return FbIdLoginRequest.from(json as FbIdLoginRequestInput);
-  }
-
-  toJson(): FbIdLoginRequestData {
-    return FbIdLoginRequestSchema.parse(this);
-  }
-}