feat: route structure, providers, layouts, and placeholder pages

app/(main)/post/[id]/page.tsx

@@ -0,0 +1,8 @@
+export default function PostDetailPage({ params: _params }: { params: Promise<{ id: string }> }) {
+  return (
+    <div className="container mx-auto py-8 px-4">
+      <h1 className="text-2xl font-bold">帖子详情</h1>
+      <p className="mt-2 text-muted-foreground">帖子内容、评论区</p>
+    </div>
+  )
+}

app/(main)/post/new/page.tsx

@@ -0,0 +1,8 @@
+export default function NewPostPage() {
+  return (
+    <div className="container mx-auto py-8 px-4">
+      <h1 className="text-2xl font-bold">发帖</h1>
+      <p className="mt-2 text-muted-foreground">发布普通帖、秀单帖或引用帖</p>
+    </div>
+  )
+}