Add GitHub Actions workflow for PR checks

This workflow runs automated checks on pull requests to ensure code
quality:

- Builds the OMG project using xcodebuild with the OMG scheme
- Validates code formatting using swiftformat with the project's
  .swiftformat configuration
- Caches Swift Package Manager dependencies to optimize build times
- Runs on all pull requests targeting main and develop branches

The workflow helps maintain code quality and consistency by catching
build failures and formatting issues before code is merged.

.github/workflows/pr-checks.yml

@@ -0,0 +1,58 @@
+name: Pull Request Checks
+
+on:
+  pull_request:
+    branches:
+      - main
+      - develop
+
+jobs:
+  build-and-format:
+    name: Build and Format Check
+    runs-on: macos-26
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Select Xcode version
+        uses: maxim-lobanov/setup-xcode@v1
+        with:
+          xcode-version: '26.1.1'
+
+      - name: Show Xcode version
+        run: xcodebuild -version
+
+      - name: Cache Swift Package Manager
+        uses: actions/cache@v4
+        with:
+          path: |
+            .build
+            ~/Library/Developer/Xcode/DerivedData
+          key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
+          restore-keys: |
+            ${{ runner.os }}-spm-
+
+      - name: Resolve Swift Package dependencies
+        run: xcodebuild -resolvePackageDependencies -project OMG.xcodeproj -scheme OMG
+
+      - name: Build OMG
+        run: |
+          xcodebuild build \
+            -project OMG.xcodeproj \
+            -scheme OMG \
+            -configuration Debug \
+            -destination 'platform=macOS' \
+            | xcpretty || exit 1
+        continue-on-error: false
+
+      - name: Install swiftformat
+        run: brew install swiftformat
+
+      - name: Check code formatting
+        run: |
+          swiftformat --lint .
+          if [ $? -ne 0 ]; then
+            echo "❌ Code formatting issues detected. Please run 'swiftformat .' locally to fix."
+            exit 1
+          fi