feat: broadcast notes to inbox relays of mentioned pubkeys

[barrydeen]

Summary

• When publishing a kind-1 note (root or reply) that mentions pubkeys via nostr: references, also deliver the event to each mentioned pubkey's read (inbox) relays per NIP-65.
• Inbox URLs are deduplicated across all mentioned pubkeys (and against our own write relays) so shared inboxes only receive the event once.
• Works for both the standard publish path (ComposeViewModel) and the background PoW mining path (PowManager).

Changes

• OutboxRouter.publishToInbox gains a Collection<String> overload that unions the read relays of every target pubkey and dedupes URLs before sending.
• ComposeViewModel.publishNote builds inboxPubkeys = replyTo.pubkey + extractedMentions and uses it for both direct publish and PoW handoff.
• PowManager.submitNote accepts an inboxPubkeys collection (defaulting to replyToPubkey for backwards compatibility).

Test plan

• Publish a root note mentioning two users whose inbox relays overlap — verify the note reaches each distinct inbox relay exactly once.
• Publish a reply that also mentions a third party — verify reply target and mentioned user both receive via their inbox relays.
• Publish a note with PoW enabled — same checks apply after mining completes.
• Publish a note with no mentions or reply target — behaviour unchanged (write-relays only).