Add outbound NIP-17 private messaging: build the kind-14 rumor -> kind-13
seal -> kind-1059 gift wrap chain on the existing NIP-44 primitives, wrapped
in NostrDmActor (WrapDirectMessage/GiftWrapped). Publishing is left to
NostrPublishActor.
Extract nostrEventId() from signNostrEvent so the unsigned rumor can compute
its id without a signature. Export the new actor and nip17 helpers. Add a
round-trip test (wrap -> unwrap) and a negative decryption test.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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