Implement taker bounty acceptance

[guildm4ster]

Requires #9

[jihadMo]

I have implemented taker bounty acceptance for SatCode using NIP-78 custom app data events (kind 30078). Added createBountyAcceptanceEvent and validateBountyAcceptanceEvent in src/nostr/acceptance.ts to bind the taker pubkey to the bounty ID, along with unit tests in acceptance.test.ts.

Fix branch: https://github.com/jihadMo/capgo/tree/fix/taker-bounty-acceptance