Add GitHub Actions CI workflow

Runs build and tests with -race on every push to main and PR.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: myleshorton

.github/workflows/ci.yml

@@ -0,0 +1,26 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go-version: ['1.24']
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version: ${{ matrix.go-version }}
+
+      - name: Build
+        run: go build ./...
+
+      - name: Test
+        run: go test -race -count=1 -timeout 60s ./...