feat: add login page and API

app/api/login/route.ts

@@ -0,0 +1,23 @@
+// app/api/login/route.ts
+import { NextResponse } from 'next/server';
+import { AUTH_USERNAME, AUTH_PASSWORD, COOKIE_NAME, COOKIE_MAX_AGE } from '@/lib/constants';
+
+export async function POST(request: Request) {
+  const body = await request.json();
+  const { username, password } = body;
+
+  if (username === AUTH_USERNAME && password === AUTH_PASSWORD) {
+    const response = NextResponse.json({ success: true });
+    response.cookies.set(COOKIE_NAME, 'ok', {
+      httpOnly: true,
+      maxAge: COOKIE_MAX_AGE,
+      path: '/',
+    });
+    return response;
+  }
+
+  return NextResponse.json(
+    { error: 'Invalid credentials' },
+    { status: 401 }
+  );
+}