feat(chapter3): replicate styled Next.js app setup

Add the App Router page group, nested layouts, Tailwind and shadcn styling, shared header components, local fonts and backgrounds, Ant Design demo support, and compatible lint scripts and dependencies.

chapter3/src/app/styles/tailwind/base.css

@@ -0,0 +1,50 @@
+/********************************************************* 自定义tailwind基本样式 *********************************************************/
+
+@layer base {
+    html {
+        font-size: 100%;
+    }
+
+    /* 以下为自定义样式 */
+    html,
+    body {
+        @apply font-base h-[100vh] w-full p-0 m-0;
+    }
+
+    body {
+        @apply text-sm;
+    }
+
+    h1 {
+        @apply text-3xl;
+    }
+
+    h2 {
+        @apply text-2xl;
+    }
+
+    h3 {
+        @apply text-xl;
+    }
+
+    h4 {
+        @apply text-lg;
+    }
+
+    h5 {
+        @apply text-sm;
+    }
+
+    h6 {
+        @apply text-xs;
+    }
+
+    button,
+    [role='button'] {
+        cursor: pointer;
+    }
+
+    :disabled {
+        cursor: default;
+    }
+}