Add GitHub Actions build and test gate

.github/workflows/ci.yml

@@ -0,0 +1,29 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  build-and-test:
+    runs-on: windows-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: 10.0.x
+
+      - name: Restore
+        run: dotnet restore GameList.sln
+
+      - name: Build (warnings as errors)
+        run: dotnet build GameList.sln --no-restore -warnaserror
+
+      - name: Test
+        run: dotnet test GameList.Tests/GameList.Tests.csproj --no-build --verbosity normal