Add GitHub Actions build workflow for PR verification

Co-authored-by: jamesmontemagno <1676321+jamesmontemagno@users.noreply.github.com>

Author: Copilot

.github/workflows/build.yml

@@ -0,0 +1,28 @@
+name: Build
+
+on:
+  pull_request:
+    branches: [ main ]
+  push:
+    branches: [ main ]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Setup .NET
+      uses: actions/setup-dotnet@v4
+      with:
+        dotnet-version: '10.0.x'
+
+    - name: Restore dependencies
+      run: dotnet restore src/TinyShop.sln
+
+    - name: Build
+      run: dotnet build src/TinyShop.sln --no-restore --configuration Release