Org upkeep (.github#1): lint baseline, Go 1.27.1, tool pins, core v0.1.5, JSON logs off a terminal

[CMGS]

Implements the per-repo part of cocoonstack/.github#1: revive default rules, nolintlint, Go 1.27.1, the pinned tool versions, projecteru2/core v0.1.5 and JSON log records when stderr is not a terminal (only the sections that apply here).

Commits

• e85e0c9 lint: enable revive default rules
• 8a11086 lint: enable nolintlint, drop unused directives
• 99594a9 build: go 1.27.1
• f30edcb build: goreleaser v2.18.2
• c87d91e deps: projecteru2/core v0.1.5

Notes

• core v0.1.5 moves only indirect lines (sentry-go, genproto/rpc, grpc).
• The JSON-off-terminal change arrives through cocoon-common: a build: bump cocoon-common commit is added here after cocoon-common's PR merges. Until then this PR keeps the v0.3.4 pin.

Gates

Run with GOWORK=off against the pinned golangci-lint v2.13.2 (built with go1.27.1):

fmt-check PASS
lint PASS
asl-linux PASS
asl-darwin PASS
test PASS
build PASS

gofumpt v0.12.0 / goimports v0.50.0 are held until the next golangci-lint release vendors them (see the issue).