chore(ci): apply L1-L5 CI-speedup pattern (via scitex-dev CLI)

[ywatanabe1989]

Generated by scitex-dev ecosystem ci-template apply (PR #159). CI-green is merge gate.

[ywatanabe1989]

Closing as superseded — fleet PR/Issue backlog sweep, 2026-08-11.

What this PR attempted: apply the L1-L5 CI-speedup pattern.

Why it is being closed: it belonged to a fleet-wide sweep opened on 2026-06-12 (59 days ago) that was never merged in this repo. That subject has since been reworked by later generations of the same change — on the repos sampled, today's default branch already carries the intended shape, or has moved to the org-level reusable workflow entirely. The premise this PR was written against no longer describes this repo.

Nothing is deleted. Branch chore/ci-speedup still holds every commit, and this PR can be reopened. An old PR assumes a codebase that has since moved, so re-doing this against today's default branch is faster and safer than rebasing a 59-day-old sweep.