Replace demo checkout with real manual bank-transfer + QR payment flow

[Copilot]

The existing checkout was explicitly labeled as a demo with no real payment intent. This replaces it with a real manual bank-transfer flow: buyers see actual transfer details, a scannable QR code, and a post-payment confirmation form — no card processing involved.

No changes were implemented in this session due to quota exhaustion. The following describes the intended changes that remain to be made:

Payment methods

• Rename Banki átutalás → Banki átutalás QR-kóddal; make it the default selected method
• Remove all "demo", "szimulált", "nincs élő terhelés" language from the transfer path
• Keep Kártya demo clearly labeled as demo (local-only validation, no gateway)

Currency selection (transfer only)

• Add HUF / EUR / USD radio group, shown when transfer is selected
• HUF: fixed HUF prices; account 30200014-19913410-90015751; transfer-data QR (labeled as data helper, not a bank-standard payment QR)
• EUR: fixed EUR prices; IBAN HU06302000141991341090015751; standards-compliant EPC/SEPA (GiroCode) QR payload
• USD: IBAN shown; prominently gated — submit disabled with actionable message until SWIFT/BIC is configured

QR generation

• Vendor qrcodejs (MIT, ~20 KB, no CDN/tracking) as scripts/qrcode.min.js
• EUR payload follows EPC069-12 v002: BCD\n002\n2\nSCT\n\nHutóczky József\n{IBAN}\nEUR{amount}\n\n\n{orderRef}
• HUF payload is plain-text transfer data; QR note explicitly states it is not a bank-standard payment QR

Order reference & confirmation form

• createOrderReference() already generates a session-scoped FX-YYYYMMDD-XXXXXX ID
• Reference propagated to: checkout summary, transfer details panel, QR payload, and confirmation form prefill
• Confirmation form (step 2) and endpoint privacy model unchanged

README

• Document real transfer flow vs. demo
• Clarify: QR scan only pre-fills banking app; customer approves transfer; activation is not automatic without a backend
• Note USD SWIFT/BIC limitation explicitly