Pin node images to the checked-out source tree (node-26#19)

Nodes checked out v1 code but pulled :latest/:stable images built from main.
Each image is now tagged src-<git tree hash of its build directory>: CI adds
that tag in every build-*.yml, and scripts/image-tags.sh computes the same
value on the node and writes it into .env as DRB_TAG_*, which
docker-compose.yml uses (falls back to :latest/:stable for local dev).
Tree hashes stay exact even though each image only rebuilds when its own
directory changes.

- install.sh pins after checkout and fails loudly if a pinned image is
  missing (compose pull only warns for services with a build: section).
- drb-update.sh pulls the target commit's pinned images BEFORE checkout,
  using the target's own compose file, so a missing image changes nothing
  (uvicorn --reload would otherwise run new code on old images). It then
  checks out, writes the pins, recreates, and removes superseded src- tags.
- New "Release images" workflow (v* tags + manual dispatch) builds any
  src- image a release ref is missing; it skips ones already published.

The live v1 tag is not moved.

Refs #19

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/release-images.yml

@@ -0,0 +1,87 @@
+name: Release images
+
+# Make sure every node image a release ref needs exists in the registry
+# (node-26#19). A node on `v1` pulls <image>:src-<tree hash of that image's
+# directory at v1>. The per-image build workflows only run when their own
+# directory changes on main, and anything built before #19 has no src- tag at
+# all, so a release tag can point at trees nobody ever built. This fills the
+# gaps: for each image, if src-<tree> is already in the registry it does
+# nothing; otherwise it builds and pushes it (registry cache keeps op25 off a
+# full recompile when only its app code changed).
+#
+# Runs on every v* tag push, including a re-cut `v1`. Also runnable by hand
+# (workflow_dispatch) on any ref — run it once on the ref `v1` points at
+# before re-cutting `v1` onto a commit that contains #19, so nodes never see
+# a moment where their pinned images don't exist yet.
+#
+# Pushes ONLY src- tags. :latest / :stable keep tracking main, as before.
+
+on:
+  workflow_dispatch:
+  push:
+    tags:
+      - "v*"
+
+jobs:
+  ensure:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - name: edge-node
+            context: drb-edge-node
+          - name: icecast
+            context: icecast
+          - name: op25-client
+            context: op25-container
+          - name: secondary-sdr
+            context: secondary-sdr-container
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-qemu-action@v3
+
+      - uses: docker/setup-buildx-action@v3
+        with:
+          config-inline: |
+            [registry."git.vpn.cusano.net"]
+              http = false
+              insecure = false
+
+      - uses: docker/login-action@v3
+        with:
+          registry: git.vpn.cusano.net
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.BUILD_TOKEN }}
+
+      - name: Resolve source tag
+        id: meta
+        run: |
+          REPO_NAME="$(echo ${GITHUB_REPOSITORY} | awk -F'/' '{print $2}')"
+          # Must match scripts/image-tags.sh and the build-*.yml workflows.
+          IMAGE="git.vpn.cusano.net/${{ vars.DOCKER_ORG }}/${REPO_NAME}/${{ matrix.name }}"
+          TAG="src-$(git rev-parse HEAD:${{ matrix.context }})"
+          echo "IMAGE=$IMAGE" >> $GITHUB_OUTPUT
+          echo "TAG=$TAG" >> $GITHUB_OUTPUT
+          if docker buildx imagetools inspect "$IMAGE:$TAG" >/dev/null 2>&1; then
+            echo "EXISTS=true" >> $GITHUB_OUTPUT
+            echo "$IMAGE:$TAG already published — nothing to do"
+          else
+            echo "EXISTS=false" >> $GITHUB_OUTPUT
+            echo "$IMAGE:$TAG missing — building it"
+          fi
+
+      - if: steps.meta.outputs.EXISTS != 'true'
+        uses: docker/build-push-action@v6
+        with:
+          context: ./${{ matrix.context }}
+          file: ./${{ matrix.context }}/Dockerfile
+          # arm64 only, same as the build-*.yml workflows (node-26#28).
+          platforms: linux/arm64
+          push: true
+          tags: ${{ steps.meta.outputs.IMAGE }}:${{ steps.meta.outputs.TAG }}
+          cache-from: type=registry,ref=${{ steps.meta.outputs.IMAGE }}:buildcache