Add GitHub Actions CI workflow (#6)

Run `bun run check` (lint, typecheck, unit tests, integration tests)
on every pull request.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: henrikje

.github/workflows/check.yml

@@ -0,0 +1,28 @@
+name: Check
+
+on:
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - uses: oven-sh/setup-bun@v2
+
+      - name: Install BATS
+        run: |
+          git clone --depth 1 https://github.com/bats-core/bats-core.git /tmp/bats-core
+          sudo /tmp/bats-core/install.sh /usr/local
+
+      - name: Configure git
+        run: |
+          git config --global user.name "CI"
+          git config --global user.email "ci@localhost"
+
+      - run: bun install
+
+      - run: bun run check