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/chat/chat_send_response.ts

@@ -1,22 +0,0 @@
-/**
- * 发送消息响应
- * 原始 Dart: ChatSendResponse (lib/data/models/chat/chat_response.dart)
- */
-import { z } from "zod";
-
-export const ChatSendResponseSchema = z.object({
-  mode: z.string().default(""),
-  reply: z.string(),
-  voiceUrl: z.string().default(""),
-  audioUrl: z.string().default(""),
-  intimacyChange: z.number().default(0),
-  newIntimacy: z.number().default(0),
-  relationshipStage: z.string(),
-  currentMood: z.string().default(""),
-  messageId: z.string(),
-  isGuest: z.boolean().default(false),
-  timestamp: z.number().default(0),
-});
-
-export type ChatSendResponseInput = z.input<typeof ChatSendResponseSchema>;
-export type ChatSendResponseData = z.output<typeof ChatSendResponseSchema>;