feat: add Gitea Actions CI pipeline

Matrix build: Python 3.11, 3.12, 3.13.
Runs ruff lint and pytest on push/PR to master.

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

.gitea/workflows/ci.yml

@@ -0,0 +1,20 @@
+name: CI
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.11", "3.12", "3.13"]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - run: pip install -e . && pip install pytest ruff
+      - run: ruff check src/ tests/ plugins/
+      - run: pytest -v