CI: actually run the tests, and let them gate the image

The image build runs 'mvn -DskipTests' and the workflow was only build -> Trivy -> push, so
no app test has ever run in CI — only Trivy gated a merge. The platform contract tests added
in 0.1.9 were not running either, which defeated their purpose.

They cannot run inside 'docker build' — Testcontainers needs a Docker daemon and a build has
none. Maven runs as a sibling container instead, mounting the workspace volume act_runner
gave this job (matched on GITHUB_WORKSPACE, since it is mounted at the full repo path rather
than at /workspace) and sharing the host network so published test ports resolve as localhost.

Verified on itsthevine before rolling out here: 33 tests ran, and a deliberately failing test
failed the run at the Test step with the registry digest unchanged — no image published.

.gitea/workflows/build.yml

@@ -15,6 +15,40 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # Tests run BEFORE the image is built, and they gate it.
+      #
+      # They cannot run inside `docker build` — Testcontainers needs a Docker daemon and there is none
+      # in a build. So Maven runs as a sibling container instead, mounting the volume act_runner gave
+      # this job (discovered from our own container rather than guessed) and sharing the host network so
+      # the ports Testcontainers publishes are reachable as localhost.
+      # Tests run BEFORE the image and gate it.
+      #
+      # They cannot run inside `docker build` — Testcontainers needs a Docker daemon and a build has
+      # none. Maven runs as a sibling container instead, mounting the volume act_runner gave this job
+      # and sharing the host network so the ports Testcontainers publishes are reachable as localhost.
+      #
+      # The volume is mounted at the full repo path, not at /workspace, so it is matched on
+      # GITHUB_WORKSPACE rather than a guess.
+      - name: Test
+        run: |
+          set -euo pipefail
+          VOL=$(docker inspect "$(hostname)" \
+            --format "{{range .Mounts}}{{if eq .Destination \"$GITHUB_WORKSPACE\"}}{{.Name}}{{end}}{{end}}")
+          if [ -z "$VOL" ]; then
+            echo "could not find this job's workspace volume — refusing to skip the tests" >&2
+            exit 1
+          fi
+          echo "workspace volume: $VOL"
+          docker run --rm --network host \
+            -v "$VOL":/w \
+            -v /var/run/docker.sock:/var/run/docker.sock \
+            -e TESTCONTAINERS_RYUK_DISABLED=true \
+            -e MAVEN_USER="${{ secrets.REGISTRY_USER }}" \
+            -e MAVEN_TOKEN="${{ secrets.REGISTRY_TOKEN }}" \
+            -w /w \
+            maven:3.9-eclipse-temurin-25 \
+            mvn -B -ntp -s .gitea/ci-settings.xml -DskipFrontend=true verify
+
       - name: Log in to the Gitea container registry
         run: echo "${{ secrets.REGISTRY_TOKEN }}" | docker login git.thebennett.net -u "${{ secrets.REGISTRY_USER }}" --password-stdin