feat: judge, sign and verify netOrk's images in one place (NetOrk/netork#1390)

The CIS gate, the SBOM, the cosign signature and the matcher's verdict lived
in NetOrk/base-os, the head of the chain. Every link below it -- base-python,
engine, ui, satellite, the service images -- needs the same, so the tools
move here, and every image repository pins them by commit.

- image_tools: cis.py, cis_os.sh, sbom.py and verify.py from base-os. The
  image's own repository holds its cis.toml and packages.allow; both default
  to the working directory.
- bin/sign.sh signs whatever platforms a reference holds: base-os's index of
  amd64 and arm64 (EXPECT_PLATFORMS) or a dev image's single manifest
  (image_tools/platforms.py).
- bin/verify-base.sh checks every FROM image of a Dockerfile against
  cosign.pub before a build; one without a digest is refused
  (image_tools/dockerfile.py).
- bin/install-cosign.sh installs cosign v3.1.3 for amd64 and arm64 runners,
  checked against the release checksums.
- actions/verify-base, judge, sign wrap them for the workflows.
- cosign.pub is the public half of the COSIGN_PRIVATE_KEY_B64 org secret,
  the key rotated on 2026-10-22.

actions/judge/action.yml

@@ -0,0 +1,45 @@
+name: Judge an image
+description: >-
+  The CIS gate (image_tools/cis.py) and the CycloneDX SBOM (image_tools/sbom.py)
+  of one platform image, kept as <out>/cis-<arch>.json, cis-<arch>.md and
+  sbom-<arch>.cdx.json for bin/sign.sh. The step fails when CIS is red.
+inputs:
+  image:
+    description: The image to judge, as Docker can run it (local tag or reference)
+    required: true
+  arch:
+    description: Its platform, amd64 or arm64
+    required: true
+  decisions:
+    description: The image repository's CIS decisions
+    default: cis.toml
+  packages:
+    description: The packages the image may hold
+    default: packages.allow
+  out:
+    description: Where the results go
+    default: attest
+runs:
+  using: composite
+  steps:
+    - name: CIS
+      shell: bash
+      env:
+        IMAGE: ${{ inputs.image }}
+        ARCH: ${{ inputs.arch }}
+        DECISIONS: ${{ inputs.decisions }}
+        PACKAGES: ${{ inputs.packages }}
+        OUT: ${{ inputs.out }}
+        PYTHONPATH: ${{ github.action_path }}/../..
+      run: |
+        mkdir -p "$OUT"
+        python3 -m image_tools.cis "$IMAGE" --decisions "$DECISIONS" --packages "$PACKAGES" \
+          --json "$OUT/cis-$ARCH.json" --report "$OUT/cis-$ARCH.md"
+    - name: SBOM
+      shell: bash
+      env:
+        IMAGE: ${{ inputs.image }}
+        ARCH: ${{ inputs.arch }}
+        OUT: ${{ inputs.out }}
+        PYTHONPATH: ${{ github.action_path }}/../..
+      run: python3 -m image_tools.sbom "$IMAGE" "$OUT/sbom-$ARCH.cdx.json"