Add CI workflow for linting, tests, and coverage

GitHub Actions workflow that runs on push/PR to main:
- golangci-lint via golangci-lint-action
- Unit tests with race detector
- Coverage report with 40% threshold (CLI integration tests
  run via exec.Command and don't register with go cover)

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

Author: schigh

.github/workflows/ci.yml

@@ -0,0 +1,42 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.23"
+      - uses: golangci/golangci-lint-action@v6
+        with:
+          version: latest
+
+  test:
+    name: Test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.23"
+
+      - name: Run library tests with coverage
+        run: go test -race -coverprofile=coverage.out -covermode=atomic ./...
+
+      - name: Report coverage
+        run: |
+          go tool cover -func=coverage.out
+          COVERAGE=$(go tool cover -func=coverage.out | grep total | awk '{print $3}' | tr -d '%')
+          echo "Total coverage: ${COVERAGE}%"
+          if [ "$(echo "$COVERAGE < 40" | bc)" -eq 1 ]; then
+            echo "::error::Coverage ${COVERAGE}% is below 40% threshold"
+            exit 1
+          fi