ci: set up CI pipeline with unit, backend, and E2E test jobs

- Add unit-tests job using Playwright Docker image (no apt install needed)
- Add backend-unit-tests job with Java 21 + Maven
- Add e2e-tests job: PostgreSQL + MinIO via docker-compose, Spring Boot backend,
  SvelteKit dev server, Playwright Chromium
- Use non-conflicting host ports (DB: 15432, MinIO: 19000/19001)
- Install Docker CLI via official Docker apt repo (Playwright image has no daemon)
- Connect job container to archive-net for direct DB/MinIO access
- Pin DOCKER_API_VERSION=1.43 for Docker socket compatibility
- Start backend with java -jar + health-check loop (curl /actuator/health)
- Use continue-on-error on cleanup step to handle SIGKILL gracefully
- Downgrade upload-artifact to v3 (v4 not supported on self-hosted Gitea)
- Always run npm ci unconditionally (actions/cache@v4 broken on this runner)
- Log /tmp/backend.log on startup timeout so Spring Boot errors are visible
- Add diagnostic steps for DB tables and Flyway schema history

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

docker-compose.ci.yml

@@ -0,0 +1,18 @@
+# CI override — replaces host bind mounts with ephemeral named volumes.
+# Host port bindings are handled via PORT_DB/PORT_MINIO_API env vars in ci.yml
+# (set to non-standard ports to avoid conflicts with system services on the runner).
+#
+# Usage:
+#   docker compose -f docker-compose.yml -f docker-compose.ci.yml up -d db minio create-buckets
+services:
+  db:
+    volumes:
+      - ci_postgres_data:/var/lib/postgresql/data
+
+  minio:
+    volumes:
+      - ci_minio_data:/data
+
+volumes:
+  ci_postgres_data:
+  ci_minio_data: