ci: run the backend test suite on pull requests

Upstream PRs currently surface only the DCO/CLA app checks, so backend
results were only ever a local report. This adds a minimal workflow that
runs ./mvnw test (Temurin 21, Maven cache, Testcontainers on the hosted
runner) for pull requests and for the authoring feature branches, making
the suite's outcome a visible check on the PR head. Happy to drop or
rework it if the maintainers prefer a different CI arrangement.

Signed-off-by: zjncs <18910855655@163.com>

.github/workflows/backend-tests.yml

@@ -0,0 +1,24 @@
+name: backend-tests
+
+# Backend test suite for pull requests. Testcontainers-based tests need a
+# Docker daemon, which the GitHub-hosted runners provide.
+on:
+  pull_request:
+  push:
+    branches: ["feat/authoring-*"]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    timeout-minutes: 90
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 21
+          cache: maven
+
+      - name: Backend tests
+        run: cd server && ./mvnw -B test