Update user profile docs with passkey integration links

Post-merge updates to user docs may have stale links. Cross-reference the new passkeys section from auth/ and add inline examples for enabling in profiles. Include a quick-setup checklist table.

What needs to be done

• Add 2-3 links and a table.
• Preview for bold consistency.

Labels: ~"group::documentation" ~"technical writing" ~"size::1"

Target MD File(s): doc/user/profile.md (check for profile settings section).

MR Guidance

1. Branch: git checkout -b update-user-profile-passkeys.
2. Edit: Add links like [Passkeys setup](../auth/passkeys.md) and table: