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/app/splash/components/splash-background.tsx

@@ -1,4 +1,17 @@
 "use client";
+/**
+ * Splash 背景图片
+ *
+ * 原始 Dart: lib/ui/splash/widgets/splash_background.dart
+ *   `SizedBox.expand(child: Assets.images.picBgHome.image(fit: BoxFit.cover))`
+ * 资源: /public/images/splash/pic-bg-home.png (kebab-case 重命名后)
+ *       原名: pic_bg_home.png (snake_case)
+ *
+ * sizes 属性说明：
+ *   图片在 MobileShell 内（max-width: 500px）。
+ *   - 视口 ≤ 500px：MobileShell = 100vw，图片 = 100vw
+ *   - 视口 > 500px：MobileShell = 500px，图片 = 500px
+ */
 import Image from "next/image";
 import styles from "./splash-background.module.css";
 
@@ -10,7 +23,7 @@ export function SplashBackground() {
         alt=""
         fill
         priority
-        sizes="100vw"
+        sizes="(max-width: 500px) 100vw, 500px"
         className={styles.image}
       />
     </div>

src/app/splash/components/splash-button.module.css

@@ -34,10 +34,11 @@
   padding: 0 30px;
   border: 0;
   border-radius: 24px;
+  /* 渐变色引用 tokens/colors.css 中定义的 token */
   background: linear-gradient(
     to right,
-    #fff96ade,
-    #fff657a0
+    var(--color-button-gradient-start),
+    var(--color-button-gradient-end)
   );
   color: #ffffff;
   font-weight: 700;