Add self-CI actionlint gate to satisfy ci/ci ruleset

The org ruleset requires the 'ci / ci' status check on every repo, but this
.github repo only houses reusable (workflow_call) workflows and emitted no such
check — so every PR sat 'Expected — Waiting for status to be reported' and was
unmergeable, including the open Dependabot bumps (#58, #59, #60).

Add a workflow that runs actionlint (pinned, checksum-verified) over the
workflow files. The ruleset matches the required check against the JOB's
check-run name, so the job is named literally 'ci / ci' to emit that exact
context (a job named 'ci' emits context 'ci', which the UI only cosmetically
shows as 'ci / ci'). shellcheck integration is disabled for now; 4 pre-existing
run-step findings are left for a separate cleanup.

Pre-existing checkov IAM findings in oidc-deploy-roles.yaml are accepted-risk
and suppressed via machine-level security-review config, intentionally NOT
committed to this repo.

.github/workflows/ci.yaml

@@ -0,0 +1,60 @@
+name: ci
+
+# Self-CI for this org `.github` repo.
+#
+# The org ruleset "main branch protection" requires the `ci / ci` status check on
+# every repo. Consumer repos satisfy it via a short caller workflow that invokes
+# the reusable workflows here. This repo only HOUSES those reusable workflows
+# (all `workflow_call`-only), so nothing emitted `ci / ci` and every PR sat
+# permanently "Expected — Waiting for status to be reported" and could not merge.
+#
+# This workflow produces that check by linting the workflow files with actionlint
+# — genuinely useful CI for a repo whose whole product is GitHub Actions YAML.
+#
+# Naming is load-bearing: the ruleset matches the required status check against
+# the JOB's check-run name, NOT "workflow / job". For a normal (non-reusable) job
+# the check-run name IS the job name, so the job must be named literally "ci / ci"
+# to emit that exact context. (A job named "ci" emits the context "ci" — which the
+# PR UI cosmetically *displays* as "ci / ci" but does NOT satisfy the requirement.)
+# This mirrors the org's aggregator-job convention.
+#
+# actionlint is pinned to a tagged release and installed by downloading the
+# release tarball and verifying its SHA256 — not `curl | bash` — to keep the
+# supply-chain surface auditable. Bump ACTIONLINT_VERSION + ACTIONLINT_SHA256
+# together (checksum from the release's *_checksums.txt).
+#
+# actionlint's shellcheck integration is disabled (`-shellcheck=`) for now: it
+# reports 4 pre-existing findings in the deploy/CI run-steps (SC2044 find-in-for
+# loops, SC2046/SC2086 quoting, one of which is intentional word-splitting in the
+# SAM deploy step). Those deserve a separate, tested cleanup rather than being
+# bundled into the gate that unblocks the repo. Re-enable shellcheck once fixed.
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  ci:
+    name: ci / ci
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Install actionlint
+        env:
+          ACTIONLINT_VERSION: 1.7.12
+          ACTIONLINT_SHA256: 8aca8db96f1b94770f1b0d72b6dddcb1ebb8123cb3712530b08cc387b349a3d8
+        run: |
+          curl -fsSL -o actionlint.tar.gz \
+            "https://github.com/rhysd/actionlint/releases/download/v${ACTIONLINT_VERSION}/actionlint_${ACTIONLINT_VERSION}_linux_amd64.tar.gz"
+          echo "${ACTIONLINT_SHA256}  actionlint.tar.gz" | sha256sum -c -
+          tar -xzf actionlint.tar.gz actionlint
+        shell: bash
+
+      - name: Lint workflows
+        run: ./actionlint -color -shellcheck=
+        shell: bash