fix(ci): tear down leftover containers before e2e run

Port 5432 was already bound by a zombie container from a previous
failed run, preventing docker compose from starting the DB.
Add a cleanup step at the top of the e2e job to ensure a clean state.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -63,6 +63,9 @@ jobs:
       - uses: actions/checkout@v4
 
       # ── Infrastructure ──────────────────────────────────────────────────────
+      - name: Cleanup leftover containers from previous runs
+        run: docker compose down --volumes --remove-orphans
+
       - name: Start DB and MinIO
         run: docker compose up -d db minio create-buckets