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/storage/chat/chat_storage.ts

@@ -18,7 +18,7 @@
 import {
   GuestChatQuotaSchema,
   type GuestChatQuotaData,
-} from "@/data/schemas/chat/guest_chat_quota";
+} from "@/data/services/schemas/chat/guest_chat_quota";
 import { z } from "zod";
 
 import { LocalStorage } from "../local_storage";

src/data/storage/chat/ichat_storage.ts

@@ -12,7 +12,7 @@
  */
 
 import type { Result } from "@/utils/result";
-import type { GuestChatQuotaData } from "@/data/schemas/chat/guest_chat_quota";
+import type { GuestChatQuotaData } from "@/data/services/schemas/chat/guest_chat_quota";
 
 export interface IChatStorage {
   getGuestDailyChatQuota(): Promise<Result<GuestChatQuotaData | null>>;

src/data/storage/user/iuser_storage.ts

@@ -12,7 +12,7 @@
  */
 
 import type { Result } from "@/utils/result";
-import type { UserData } from "@/data/schemas/user/user";
+import type { UserData } from "@/data/services/schemas/user/user";
 
 export interface IUserStorage {
   getUser(): Promise<Result<UserData | null>>;

src/data/storage/user/user_storage.ts

@@ -15,7 +15,7 @@
  *   - 单例挂在 class 静态字段，HMR 复用安全
  */
 
-import { UserSchema, type UserData } from "@/data/schemas/user/user";
+import { UserSchema, type UserData } from "@/data/services/schemas/user/user";
 import { LocalStorage } from "../local_storage";
 import { type Result as ResultT } from "@/utils/result";
 import { StorageKeys } from "../storage_keys";