Add a translation seam for user-facing strings (i18n) #6

All user-facing text in the connect UI is currently hardcoded English: the button label, the modal title ("Connect a wallet"), the pending and empty states, and the connect-error messages (WalletLinkButton.tsx, WalletLinkModal.tsx, describeConnectError in internal.tsx).

Deferred from the connect-UI PR review (raised by CodeRabbit). English-only is acceptable for the first release; this issue tracks exposing a translation seam later once the component API has settled.

Likely shape when we pick this up: a messages object or a t() callback prop so consumers can override every string, defaulting to the current English copy.