bug: import with pubky ring fails after authorize

[ovitrif]

What happened?

"Import with Pubky Ring" fails after the user taps Authorize in Pubky Ring. Bitkit hands the Paykit grant request to Ring as a legacy sign-in, so Ring answers with a legacy auth token and Bitkit's grant flow rejects it. The profile and contacts are never imported.

PubkyRingAuthURLBuilder.ringHandoffURL (Bitkit/Managers/PubkyProfileManager.swift) sets the host of every handoff link to signin. That rewrites signin_grant requests, dropping their grant intent, while Pubky Ring 1.19 already handles pubkyring://signin_grant.

Expected behavior

The handoff keeps the grant intent (pubkyring://signin_grant, including its cid/cpk parameters). Ring then approves a grant, Bitkit accepts it, and "Found profile & contacts" appears.

Steps to Reproduce

1. Install Pubky Ring 1.19 or later, holding a key with a Pubky App profile and at least one follow.
2. In Bitkit, open Profile and choose "Import with Pubky Ring".
3. In Ring, tap Authorize.
4. Back in Bitkit: the import fails instead of showing "Found profile & contacts".

Logs / Screenshots / Recordings

• Found by reading the handoff code and confirmed with an offline check of the handoff URL against Ring's handler. It has not yet been reproduced end to end on a device.
• A fix that keeps signin_grant on the handoff, with a unit test for it, passes the unit tests on a demo branch and can be opened as a PR.
• Overlap: feat: use pubky ring keys via shared keychain #774 removes this rewrite as part of the shared-keychain Ring flow. If feat: use pubky ring keys via shared keychain #774 lands first, this issue closes with it.

Bitkit Version

master at 69a85df

Device / OS

iOS Simulator, iOS 26.5, with a Pubky Ring 1.19 Release build

Reproducibility

Always, whenever the auth request is a signin_grant.