Org upkeep (.github#1): Go 1.27.1, Rust 1.98.1, goreleaser pin, core v0.1.5, JSON logs off a terminal, control-plane lint

[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

• 3b99e7d build: go 1.27.1
• eb255ce build: goreleaser v2.18.2
• db6c2f3 log: JSON records when stderr is not a terminal
• ab6a58b build: rust 1.98.1
• 1cacbf7 deps: projecteru2/core v0.1.5
• e180bea docs: package comment for the control-plane entry point
• 915a937 lint: golangci-lint for control-plane

Notes

• control-plane joins the family lint baseline: the shared .golangci.yml (one extra exclusion: goconst under internal/gateway/mock/, fixture strings), a make lint target that loops linux/darwin over ./... and --build-tags integration ./internal/integration, and CI runs it. The 17 findings are fixed in the same commit; the two cookie gosec hits are nolinted because Secure follows the documented CP_COOKIE_SECURE (default unchanged), and the argon2 key length is bounded two lines above its cast.
• run()'s shutdown closure keeps its own shutdownErr: it runs concurrently with ListenAndServe, so reusing the named return would race.
• core v0.1.5 requires golang.org/x/crypto v0.56.0, which lifts control-plane's direct requirement from v0.55.0; sentry-go and genproto/rpc move as indirect lines.
• Rust 1.98.1: channel, rust-version and the Dockerfile base (digest from crane digest rust:1.98.1) move together.

JSON logs off a terminal

control-plane: stderr to a file gives {"level":"info","func":"main.run",...}; under script -q the console line has ANSI colour codes.

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
vet PASS
test PASS
build PASS
rust PASS

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