ci: hard-fail PR and release scans on unacknowledged HIGH/CRITICAL CVEs (#484)

* ci: hard-fail PR and release scans on unacknowledged HIGH/CRITICAL CVEs

Make Trivy a real gate instead of an advisory signal:

- PR CI (docker-validate) no longer uses `continue-on-error: true` on the
  Trivy step, so any HIGH/CRITICAL finding not in `.trivyignore` fails the PR.
- The release pipeline (docker-publish.yml) now builds an amd64-only scan
  image into the local daemon before the multi-arch push-build, re-runs
  Trivy against that exact artifact, and only proceeds to the push if the
  scan passes. This closes the gap where a CVE landed between PR merge and
  release-time rebuild.
- New `.trivyignore` at repo root is the single source of truth for
  acknowledged CVEs across both workflows; it starts empty so the first CI
  run surfaces the full list, which we then populate with justifications.

* ci: populate .trivyignore with initial HIGH/CRITICAL acknowledgements

First CI run on the hard-fail Trivy policy surfaced 7 unacknowledged
findings. Each has been reviewed and justified inline:

- 6 CVEs in the statically-linked Go modules inside docker-compose v5.1.1
  (github.com/docker/docker, buildkit, otel/sdk x2, grpc). These are
  transitively bundled and cannot be bumped without an upstream Compose
  rebuild. The grpc CVE is already explicitly acknowledged in the
  Dockerfile rationale block at Dockerfile:108-111.
- 1 CVE in picomatch 4.0.3 bundled inside the npm CLI that ships with
  node:22-alpine. npm is only invoked at build time against our own
  package.json, so the ReDoS vector is not reachable.

Every entry has a revisit trigger (next Compose release or next Alpine
node bump).

.trivyignore

@@ -0,0 +1,87 @@
+# Trivy ignore list
+#
+# Every entry in this file is a known HIGH or CRITICAL CVE that we have
+# consciously accepted risk on and decided not to block CI over. Format:
+#
+#   CVE-YYYY-NNNNN
+#   # Justification: why we're accepting this risk, and a link or note about
+#   # when to revisit (e.g. "blocked on upstream base image update, revisit
+#   # when alpine/node:22 ships a fix").
+#
+# Rules:
+#   - Every CVE MUST have a justification comment directly above it.
+#   - If there is no justification, the CVE is not ignored - add it here only
+#     after a human review and a decision to accept the risk.
+#   - Review this file on every release; remove entries whose upstream fix has
+#     landed.
+#
+# Picked up automatically by aquasecurity/trivy-action from the repo root
+# working directory. Both the pre-push PR scan (.github/workflows/ci.yml) and
+# the release-time re-scan (.github/workflows/docker-publish.yml) honor it.
+
+# ---------------------------------------------------------------------------
+# Bundled inside /usr/local/lib/docker/cli-plugins/docker-compose (v5.1.1)
+# ---------------------------------------------------------------------------
+# Compose v5.1.1 is the latest upstream release and is already pinned in
+# Dockerfile:113 to get us off the v2.40.3 grpc 1.74.2 / x/crypto 0.38.0 CVE
+# set. It statically links older copies of github.com/docker/docker,
+# buildkit, otel, and grpc. We cannot bump these transitively without
+# waiting for a new upstream Compose release. Revisit this block on every
+# Compose release; remove entries as upstream rebuilds ship the fixes.
+# See the rationale block at Dockerfile:96-111.
+
+# Justification: github.com/docker/docker v28.5.2 statically bundled in
+# compose v5.1.1. Moby authz bypass applies to a Docker daemon, not to the
+# compose CLI plugin; compose never runs as a daemon. Revisit on next
+# Compose upstream release.
+CVE-2026-34040
+
+# Justification: github.com/moby/buildkit v0.27.1 statically bundled in
+# compose v5.1.1. BuildKit arbitrary file write via untrusted frontend is
+# exploited at buildkit build time with attacker-controlled frontends; our
+# compose invocations only call up/down/ps against local user-authored
+# compose files, never as a build frontend. Revisit on next Compose upstream
+# release.
+CVE-2026-33747
+
+# Justification: github.com/moby/buildkit v0.27.1 statically bundled in
+# compose v5.1.1. Same exposure profile as CVE-2026-33747 (Git URL fragment
+# subdir exploitation requires invoking buildkit on untrusted repo URLs,
+# which compose does not do in our flow). Revisit on next Compose upstream
+# release.
+CVE-2026-33748
+
+# Justification: go.opentelemetry.io/otel/sdk v1.38.0 statically bundled in
+# compose v5.1.1. PATH hijacking requires the attacker to control the
+# process PATH before compose starts; our container starts compose from a
+# fixed PATH with only /usr/local/bin and /usr/bin on it, both owned by
+# root. Revisit on next Compose upstream release.
+CVE-2026-24051
+
+# Justification: go.opentelemetry.io/otel/sdk v1.38.0 statically bundled in
+# compose v5.1.1. BSD kenv PATH hijacking only applies on BSD systems; we
+# ship linux/amd64 and linux/arm64. Not applicable in our runtime. Revisit
+# on next Compose upstream release.
+CVE-2026-39883
+
+# Justification: google.golang.org/grpc v1.78.0 statically bundled in
+# compose v5.1.1 AND in Docker CLI v29.3.1. Already explicitly acknowledged
+# in the Dockerfile rationale block at Dockerfile:108-111 as unpatched,
+# waiting on a new Docker CLI or Compose release that ships grpc >= 1.79.3.
+# Exploit requires an attacker-controlled HTTP/2 peer talking to a gRPC
+# server; compose and the docker CLI only act as gRPC clients against the
+# local unix socket, not as servers.
+CVE-2026-33186
+
+# ---------------------------------------------------------------------------
+# Bundled inside /usr/local/lib/node_modules/npm/ (node:22-alpine base image)
+# ---------------------------------------------------------------------------
+
+# Justification: picomatch 4.0.3 is shipped inside the npm CLI that comes
+# bundled with the upstream node:22-alpine base image. We do not run npm at
+# container runtime against user-controlled input; npm is only invoked at
+# build time against our own package.json files. The ReDoS requires an
+# attacker-authored extglob pattern, which is not reachable from any
+# runtime code path. Revisit when a future node:22-alpine base image ships
+# a newer npm that bundles picomatch >= 4.0.4.
+CVE-2026-33671