ci: move remaining workflows to Node 24 action runtimes

[Altairpaca]

Problem

Recent hosted-runner logs warn that DSHelm still references JavaScript actions whose declared runtime is Node 20. GitHub is already forcing those actions onto Node 24, and Node 20 is scheduled to leave hosted runners on 2026-09-16.

Change

• move general CI, first-run, and published-DSH compatibility workflows from actions/checkout@v4 to @v7;
• move those workflows from actions/setup-node@v4 to @v7 while keeping project Node 22;
• move all remaining pnpm/action-setup@v4 references to the Node-24-native @v6.1.0 while keeping pnpm 11.7.0;
• leave the npm release workflow's already-Node-24 checkout@v6 / setup-node@v6 lines unchanged to keep this migration minimal.

Scope

No Node application-runtime change, pnpm version change, package graph change, release behavior change, or DSH compatibility claim is introduced.

Closes #36