Add GitHub Actions CI workflow for cross-platform testing

- Run tests on ubuntu-latest and macos-latest
- Test platform-specific network isolation code
- Use Go 1.25 with race detection enabled
- Cache Go modules for faster builds
- Trigger on all pushes and pull requests

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: f0ssel

.github/workflows/ci.yml

@@ -0,0 +1,56 @@
+name: CI
+
+on:
+  push:
+    branches: [ main, "blink/*" ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test:
+    name: Test
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+
+    steps:
+    - name: Check out code
+      uses: actions/checkout@v4
+
+    - name: Set up Go
+      uses: actions/setup-go@v5
+      with:
+        go-version: '1.25'
+        check-latest: true
+
+    - name: Cache Go modules
+      uses: actions/cache@v4
+      with:
+        path: |
+          ~/.cache/go-build
+          ~/go/pkg/mod
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-go-
+
+    - name: Download dependencies
+      run: go mod download
+
+    - name: Verify dependencies
+      run: go mod verify
+
+    - name: Run tests
+      run: go test -v -race -coverprofile=coverage.out ./...
+
+    - name: Run build
+      run: go build -v ./...
+
+    - name: Upload coverage to Codecov (Linux only)
+      if: matrix.os == 'ubuntu-latest'
+      uses: codecov/codecov-action@v4
+      with:
+        file: ./coverage.out
+        flags: unittests
+        name: codecov-umbrella