Description of problem

4.16 left the maintenance phase and entered the EUS phase on 2025-12-27. We want 4.16.z that enter fast-4.16 up through that time to keep being added to stable-4.16, but 4.16.z that enter fast-4.16 after that date to only be added to eus-4.16 (and no longer get added to stable-4.16), to help folks who don't meet the EUS qualifications stay on releases that they have support for. I'm a bit late this time around, but catching up now, only a bit past that EUS transition. This change would give users in the default channel access to patch updates they qualify for, assuming only folks with EUS qualifications are installing 4.16.z releases during the EUS lifecycle phase.

Version-Release number of selected component

Only the 4.16 installer needs updating, to reflect this 4.16-lifecycle-phase transition.

How reproducible

Every time.

Steps to Reproduce

1. Install a 4.16.z cluster.
2. Check its current channel, e.g. with oc adm upgrade | grep Channel.

Actual results

Channel: stable-4.16 (...)

Expected results

stable-4.16 for 4.16.younger, but starting with EUS-era 4.16.larger, eus-4.16.