The shared lint config in the prompts repo moved from the deprecated
gomodguard linter to gomodguard_v2, with a module block list, and now
enables depguard to keep test-support packages out of non-test files.
This replaces the repo's copy with that file unchanged, so lint no
longer prints the gomodguard deprecation warning.
Model: opus-5-5
Bump the pinned golangci-lint from v2.12.1 to v2.12.2 in the
Dockerfile lint stage (tagged, digest-pinned Debian image) and in
script/bootstrap (go install ref). Replace .golangci.yml with the
canonical config: linter settings (lll, funlen, cyclop, dupl) move
under linters.settings per the v2 schema so they are actually
applied, and the redundant issues.exclude-use-default key is
dropped. No new lint findings surfaced; make check is green.