feat: share pubky keys between bitkit and pubky ring #813

Twin: synonymdev/bitkit-android#1355
Refs: #774

Problem or use case

Bitkit asks Pubky Ring to sign for it through a deep-link flow, and a user cannot pick one of their Pubky Ring pubkys in Bitkit.

Proposed solution

• Pubky Ring can use the pubky Bitkit created.
• The user can pick one of their Pubky Ring pubkys on Pubky Choice.
• Bitkit clears a picked pubky when Pubky Ring deletes it.
• The deep-link signing flow is removed.