ci(dylint): decide and enforce Dylint as a required status check

[zackees]

Context

#939 asked to consider making Dylint a required status check after fixing the red custom-lint gate. The enforcement bug itself is fixed by #989 and the accumulated lint violations were cleaned up in #991; Dylint is green on current main.

A branch-protection API check on 2026-07-07 returned Required status checks not enabled for main, so the remaining work is policy/admin configuration rather than Dylint build repair.

Task

Decide whether Dylint should be required for merges, and configure/document the result.

Acceptance criteria

• Decide whether Dylint should be a required status check on main.
• If yes, enable the repository branch protection/ruleset requirement for the exact Dylint check and verify it appears in the required checks list.
• If no, close this issue with the rationale so Dylint CI gate is red on main (driver build_library failure) — lints are not enforcing #939's policy request has an explicit answer.
• Link the outcome back to Dylint CI gate is red on main (driver build_library failure) — lints are not enforcing #939 and meta: reconcile residual #942/#974 follow-ups after #974 close-out #992.