feat: unify on single repo-root compose file for dev and prod

.forgejo/workflows/backend.yml

@@ -0,0 +1,22 @@
+# Backend test suite. Runs the full pytest suite on a throwaway SQLite file.
+# Prerequisites on the Forgejo instance (not verifiable from the repo):
+# - a Runner with the `docker` label online (repo Settings -> Actions -> Runners)
+# - action resolution for actions/checkout (github proxy or code.forgejo.org mirror)
+on:
+  push:
+    branches: [main]
+  pull_request:
+    paths:
+      - "backend/**"
+      - "docker-compose.yml"
+      - ".forgejo/workflows/backend.yml"
+
+jobs:
+  test:
+    runs-on: docker
+    container:
+      image: ghcr.io/astral-sh/uv:python3.12-bookworm
+    steps:
+      - uses: actions/checkout@v4
+      - run: cd backend && uv sync
+      - run: cd backend && uv run pytest