feat: integrate Stripe payment with bugfixes and active timeout cancellation

- Add Stripe payment provider with Checkout Session flow
- Payment provider abstraction layer (EasyPay + Stripe unified interface)
- Stripe webhook with proper raw body handling and signature verification
- Frontend: Stripe button with URL validation, anti-duplicate click, noopener
- Active timeout cancellation: query platform before expiring, recover paid orders
- Singleton Stripe client, idempotency keys, Math.round for amounts
- Handle async_payment events, return null for unknown webhook events
- Set Checkout Session expires_at aligned with order timeout
- Add cancelPayment to provider interface (Stripe: sessions.expire, EasyPay: no-op)
- Enable stripe in frontend payment type list

src/app/api/users/[id]/route.ts

@@ -1,10 +1,7 @@
 import { NextResponse } from 'next/server';
 import { getUser } from '@/lib/sub2api/client';
 
-export async function GET(
-  _request: Request,
-  { params }: { params: Promise<{ id: string }> },
-) {
+export async function GET(_request: Request, { params }: { params: Promise<{ id: string }> }) {
   const { id } = await params;
   const userId = Number(id);