Public BoltCard balance check and passcode-protected balances overview

Two new public-facing pages were added to the rewards app. /balance_check lets anyone tap a BoltCard via NFC to see its current balance — no login required. /balances shows all active cards with their sats balance, ZAR equivalent, division, TSK level, and Junior Coach level; it is protected by a configurable passcode.

Both pages are optimised for mobile and show card number, spending limits, and a transaction history modal. NFC permission is requested on button press to comply with browser security requirements.