Add GitHub Actions CI

Runs the existing pre-commit hooks (ruff, pyright, pytest) on push, PR,
and a twice-monthly schedule so upstream dependency breaks surface even
without a local change to the library.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: tabishm52

.github/workflows/ci.yml

@@ -0,0 +1,20 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+  schedule:
+    - cron: "0 6 1,15 * *"
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - uses: astral-sh/setup-uv@v8.2.0
+        with:
+          enable-cache: true
+      - run: uv sync
+      - run: uv run pre-commit run --all-files