epic: Pubky marketplace wallet support #1207

Related: synonymdev/bitkit-ios#712
Source: Pubky marketplace Bitkit team brief

Outcome

Track the repository work required for the Pubky marketplace phone-wallet flow. Hypercolor, Pubky Ring, Homegate, browser-seller Paykit Server work, and the BitcoinErrorLog/bitkit* forks are outside scope.

Shared completion criteria

• A marketplace seller can authorize the watch-only account claim without granting spending authority.
• A buyer who satisfies the agreed contact/trust prerequisite receives and opens a valid Paykit Payment Request.
• The issuer formats accepted by Bitkit are documented and locked down by tests.
• Rejected or unresolvable requests produce diagnosable logs and the agreed user feedback.
• A regtest marketplace wallet leg reaches an accepted, confirmed on-chain payment without reporting a dropped transaction as sent.
• Each platform has a durable journey covering its supported marketplace wallet leg.