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/dto/auth/send_code_request.ts

@@ -0,0 +1,30 @@
+/**
+ * 发送验证码请求 DTO
+ */
+import {
+  SendCodeRequestSchema,
+  type SendCodeRequestInput,
+  type SendCodeRequestData,
+} from "@/data/services/schemas/auth/send_code_request";
+
+export class SendCodeRequest {
+  declare readonly email: string;
+
+  private constructor(input: SendCodeRequestInput) {
+    const data = SendCodeRequestSchema.parse(input);
+    Object.assign(this, data);
+    Object.freeze(this);
+  }
+
+  static from(input: SendCodeRequestInput): SendCodeRequest {
+    return new SendCodeRequest(input);
+  }
+
+  static fromJson(json: unknown): SendCodeRequest {
+    return SendCodeRequest.from(json as SendCodeRequestInput);
+  }
+
+  toJson(): SendCodeRequestData {
+    return SendCodeRequestSchema.parse(this);
+  }
+}