ci: add GitHub Actions workflow running ruff + pytest on push/PR

Runs on every push to main and on every PR. Pipeline:
1. uv setup with cache
2. Python 3.12 (matches pyproject's requires-python)
3. uv sync --extra server (installs FastAPI/pydantic/etc)
4. ruff format --check . (gate)
5. pytest --cov=violetear

Mirrors `make test-unit` so local + CI behavior are identical.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: apiad

.github/workflows/tests.yml

@@ -0,0 +1,29 @@
+name: tests
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v3
+        with:
+          enable-cache: true
+
+      - name: Set up Python
+        run: uv python install 3.12
+
+      - name: Install dependencies
+        run: uv sync --extra server
+
+      - name: Check formatting
+        run: uv run ruff format --check .
+
+      - name: Run tests
+        run: uv run pytest --cov=violetear