[ flox1an/slidestr ] feat: add ZapModal with QR code fallback and UI improvements

- Add ZapModal with NWC payment and QR code fallback for non-NWC users
- Add WalletSettings component for NWC wallet connection
- Add wallet icon with balance display in header
- Add circle hover effect (30% black) to all icon buttons
- Fix Jotai Provider placement for login state updates
- Remove old Settings dialog, add new minimal WalletSettings
- Add generateInvoice function for QR code invoice generation

https://github.com/flox1an/slidestr/commit/0f5c6f479f96dc89e4bdb5ff243c46e82a615927