Investigate interaction between copilot and `serverKnownCredentialIDs`

[melvin-bot]

When switching into an account via copilot (or switching back), biometrics show as not registered until the page is refreshed. This suggests the account Onyx key dance during copilot switching may not be persisting serverKnownCredentialIDs correctly, or it needs to be re-populated after the switch.

Steps to reproduce:

1. Use copilot to switch into another account (or switch back to your own).
2. Check the biometrics registration status — it shows as not registered.
3. Refresh the page — biometrics now show as registered correctly.

Expected: Biometrics registration status reflects correctly after a copilot account switch, without requiring a page refresh.

Goal: Investigate whether the account Onyx key is dropping serverKnownCredentialIDs during copilot switches, and fix accordingly.

[chuckdries]

Backend fix is in staging

[chuckdries]

This is fixed