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/user/user.ts

@@ -1,59 +0,0 @@
-/**
- * 用户 DTO
- */
-import {
-  UserSchema,
-  type UserInput,
-  type UserData,
-} from "@/data/schemas/user/user";
-import { PersonalityTraits } from "./personality_traits";
-
-export class User {
-  declare readonly id: string;
-  declare readonly username: string;
-  declare readonly email: string;
-  declare readonly platform: string;
-  declare readonly intimacy: number;
-  declare readonly dolBalance: number;
-  declare readonly relationshipStage: string;
-  declare readonly currentMood: string;
-  declare readonly personalityTraits: PersonalityTraits;
-  declare readonly preferredLanguage: string;
-  declare readonly createdAt: string;
-  declare readonly lastMessageAt: string;
-  declare readonly avatarUrl: string;
-  declare readonly loginProvider: string;
-  declare readonly isGuest: boolean;
-
-  private constructor(input: UserInput) {
-    const data = UserSchema.parse(input);
-    Object.assign(this, {
-      ...data,
-      personalityTraits: PersonalityTraits.from(data.personalityTraits),
-    });
-    Object.freeze(this);
-  }
-
-  static from(input: UserInput): User {
-    return new User(input);
-  }
-
-  static fromJson(json: unknown): User {
-    return User.from(json as UserInput);
-  }
-
-  /**
-   * 创建一个具有空 id/username 的 User 实例（用于可选 user 字段的默认占位）
-   */
-  static empty(): User {
-    return new User({ id: "", username: "" });
-  }
-
-  toJson(): UserData {
-    const { personalityTraits, ...rest } = this;
-    return {
-      ...rest,
-      personalityTraits: personalityTraits.toJson(),
-    };
-  }
-}