refactor(lib): organize modules by feature

app/api/auth/youtube/callback/route.ts

@@ -1,6 +1,6 @@
 import { cookies } from "next/headers";
 import { NextRequest, NextResponse } from "next/server";
-import { requireAdmin } from "@/lib/auth";
+import { requireAdmin } from "@/lib/auth/auth";
 
 function escapeHtml(value: unknown) {
 	return String(value ?? "")

app/api/auth/youtube/route.ts

@@ -1,7 +1,7 @@
 import { randomBytes } from "node:crypto";
 import { cookies } from "next/headers";
 import { NextResponse } from "next/server";
-import { requireAdmin } from "@/lib/auth";
+import { requireAdmin } from "@/lib/auth/auth";
 
 const COOKIE = "youtube-oauth-state";