feat: add emails/{email_id}/share endpoint
Merged
DI
2mo ago+47+47+01234567890123456789-0-0-0123456789
Adds POST /emails/{email_id}/share — creates a shareable link for a sent or received email.
Optional body: expires_in (human-readable duration, e.g. 10m, 2 hours, 1 day; default 48h, capped at 48h).
resend.json intentionally not touched — CI regenerates it via a separate PR on merge to main, per this repo's own convention.