[ingvarch]

What changes

CI lints with the latest golangci-lint release instead of a pinned one, and make lint lints with whatever golangci-lint is installed. A pinned version fell behind the one a package manager installs, and make check stopped on the version check.

• make lint still fails when golangci-lint is not installed, and says CI lints with the latest release.
• The test on the Makefile now checks that CI asks for latest and that any installed version lints.
• golangci-lint 2.15 brings errcheck 1.30, which reports an error taken from a channel and dropped. The shell test now checks that the wait for a key ended because it was canceled. The read of where a log ends names the error it drops and says why: the stream opened next reads the same log and shows the error.
• CONTRIBUTING.md and CLAUDE.md say this.

A new golangci-lint release can now fail CI on a branch that did not change. That is the cost of always linting with the latest one.

Checklist

• The test for this change was written first and failed
• make check is green
• The title is a conventional commit: feat(ui): ..., fix(nomad): ...