docs: point the second-link sign-in journey at its ios port and fix its pin pad step #1560

Twin: synonymdev/bitkit-ios#994

Refs:

• fix: keep a pending pubky sign-in link when another link opens #1547
• fix: keep a pending pubky sign-in link when another link opens bitkit-ios#987

What happened?

journeys/pubky-auth/signin-with-second-link.xml is out of date in two places:

• Its description and the journeys/README.md row say the journey is not ported to iOS because iOS dropped the pending sign-in link (bug: a link opened on the pin screen drops a pending pubky sign-in link bitkit-ios#985). fix: keep a pending pubky sign-in link when another link opens bitkit-ios#987 has since merged with the iOS port of this journey.
• Its "Verify the PIN pad is visible (testTag "PinPad")" steps name a tag that android layout does not show; only the pad's keys (N0–N9) appear (device run).

Expected behavior

The journey and the cross-platform row point at the iOS file, and the PIN pad step checks an identifier android layout reports, in the same words as the iOS journey once synonymdev/bitkit-ios#994 aligns them.

Steps to Reproduce

1. Read the description of journeys/pubky-auth/signin-with-second-link.xml and its row in journeys/README.md.
2. Run the journey and dump android layout on the PIN screen: there is no PinPad resource-id.

Additional context

Docs only; no app change.