[ nostr-dev-kit/ndk ] fix(svelte): correct wallet store mints API to return string[]

- Changed `$wallet.mints` to return `string[]` (configured mint URLs) instead of `Mint[]`

- Added `$wallet.mintBalances` getter that returns `Mint[]` with balances (including 0 balance)

- Updated nutsack example components to use correct API

- Updated README documentation

https://github.com/nostr-dev-kit/ndk/commit/4482b628e646423264ae5216e88c259655497310