The frontend (lib/payu.ts, payu-return.tsx) and admin config UI had
already switched to PayU, but the payments service was still calling
Razorpay's order API and verifying Razorpay HMAC signatures -
payments were broken end to end. Rewrites apps/payments to PayU's
hash-based hosted-checkout flow (SHA-512 request/response hash,
key+salt from admin config or PAYU_MERCHANT_KEY/PAYU_SALT), for both
the tracecoin wallet purchase flow and the AI credits flow. The AI
credits frontend checkout was also fabricating a fake payment_id and
signature client-side instead of ever opening a real PayU checkout -
fixed to use the same real flow as tracecoin purchases.
Also fixes the ai_create_ticket endpoint on the users service, which
never validated the X-AI-Service-Key header despite the client
sending one - anyone could create tickets under an arbitrary user_id.
64089e4da3