Bumps the pinned golangci-lint from v2.12.1 to v2.12.2 in the Dockerfile
lint stage and script/bootstrap, and replaces .golangci.yml with the
canonical org-standard file (sha256
021cc83f4e6fc7c31b95b34b846723dfcf20b66b7baeea1dc40406e643346bcb).
The material change is that the lll, funlen, cyclop and dupl thresholds
move from the v1-style top-level linters-settings key, which
golangci-lint v2 silently ignores, to linters.settings, where they are
actually enforced. Independent review proved the migration claim with a
controlled experiment and confirmed the code passes the now-live
thresholds with zero findings.
Reviewed independently; make check and make docker both green.
