fix: resolve homepage 404 and add mock data for user portrait

Add landing page, fix type errors, mark dynamic API route, and refactor user portrait page.

Co-authored-by: null <4804959+fnvtk@users.noreply.github.com>

app/api/database-structure/route.ts

@@ -1,3 +1,5 @@
+export const dynamic = "force-dynamic"
+
 import { NextResponse } from "next/server"
 import { getDatabases, getDatabaseStructure } from "@/lib/mongodb-mock-connector" // 更新导入路径