Add CI on Gitea Actions: pytest and ruff on every PR

.gitea/workflows/ci.yaml runs on PRs into main and on pushes to main.
It installs uv, runs `uv sync --locked` with Python 3.12 (the lowest
version requires-python allows), then pytest, `ruff check` and
`ruff format --check`.

ruff is pinned in the dev group (0.17.3). The repo has no ruff config,
so the rules are ruff's defaults for that version; pinning makes CI
and local runs check the same rules. The setup follows the workflow
that already runs green on this Gitea instance (ubuntu-latest, pinned
checkout SHA, uv via the official script). The README gets a CI badge
and the lint commands.

Closes #11

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/ci.yaml

@@ -0,0 +1,50 @@
+name: CI
+
+# Tests and lint for every PR into main, and a status for each commit on main.
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+# Reads the repository only.
+permissions:
+  contents: read
+
+# A newer push to the same ref makes an in-flight run obsolete.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    name: pytest and ruff
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - name: Checkout
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+
+      # Same uv as local development; the official script keeps the job free of
+      # third-party actions beyond checkout.
+      - name: Install uv
+        run: |
+          curl -LsSf https://astral.sh/uv/0.13.6/install.sh | sh
+          echo "$HOME/.local/bin" >> "$GITHUB_PATH"
+
+      # --locked: fail if uv.lock does not match pyproject.toml. Python 3.12 is the
+      # lowest version requires-python allows.
+      - name: Install dependencies
+        run: uv sync --locked --python 3.12
+
+      # The tests mock cv4pve-cli: no binary and no cluster access needed.
+      - name: Tests
+        run: uv run pytest -q
+
+      # ruff is pinned in the dev group, so CI checks the same rules as local runs
+      # (no config file: ruff's own defaults for that version).
+      - name: Lint
+        run: uv run ruff check src tests
+
+      - name: Format
+        run: uv run ruff format --check src tests