tests/jetstream.rs: the store, event log and projection against a real JetStream

Until now nothing outside a live site exercised the NATS side: the
aggregate engine was tested by in-memory replay only. This test
submits an answer, moves it from a desk through the engine, checks
that an undeclared move and an unknown record are refused, and reads
the record back from its own event log. It runs when
PORTAL_TEST_NATS_URL is set; CI starts a throwaway nats:2.14.6-alpine
with JetStream for it and tears it down. Without the variable the
test passes as skipped, so `cargo test` stays green offline.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L4jrCgLiKKHAEFuZUJjckH

.gitea/workflows/test.yml

@@ -22,5 +22,22 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # A throwaway JetStream for tests/jetstream.rs. Best effort: if the
+      # runner cannot use docker the variable stays unset and that one
+      # test reports itself skipped rather than failing the build.
+      - name: Start a throwaway JetStream
+        run: |
+          docker rm -f portal-test-nats >/dev/null 2>&1 || true
+          if docker run -d --rm --name portal-test-nats -p 127.0.0.1:14223:4222 nats:2.14.6-alpine -js >/dev/null 2>&1; then
+            sleep 2
+            echo "PORTAL_TEST_NATS_URL=nats://127.0.0.1:14223" >> "$GITHUB_ENV"
+          else
+            echo "::warning::no docker on this runner - the JetStream integration test will be skipped"
+          fi
+
       - name: Test
         run: cargo test --features ssr
+
+      - name: Stop the throwaway JetStream
+        if: always()
+        run: docker rm -f portal-test-nats >/dev/null 2>&1 || true