ci: add GitHub Actions workflow to build Omega Mac app

Adds a manually-triggered workflow that builds the SwiftUI app on a
macOS 15 runner with Xcode 16, packages it as a .app bundle, and
uploads it as a downloadable artifact. Also lowers the deployment
target to macOS 14 so it runs on Sonoma.

.github/workflows/build-omega-mac.yml

@@ -0,0 +1,72 @@
+name: Build Omega Mac
+
+on:
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: macos-15
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Select Xcode
+        run: sudo xcode-select -s /Applications/Xcode_16.2.app/Contents/Developer
+
+      - name: Resolve dependencies
+        working-directory: apps/omega-mac
+        run: swift package resolve
+
+      - name: Build release
+        working-directory: apps/omega-mac
+        run: swift build -c release
+
+      - name: Package .app bundle
+        working-directory: apps/omega-mac
+        run: |
+          mkdir -p OmegaMac.app/Contents/MacOS
+          mkdir -p OmegaMac.app/Contents/Resources
+          cp .build/release/OmegaMac OmegaMac.app/Contents/MacOS/OmegaMac
+
+          cat > OmegaMac.app/Contents/Info.plist << 'PLIST'
+          <?xml version="1.0" encoding="UTF-8"?>
+          <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+          <plist version="1.0">
+          <dict>
+            <key>CFBundleExecutable</key>
+            <string>OmegaMac</string>
+            <key>CFBundleIdentifier</key>
+            <string>com.tpmjs.omega-mac</string>
+            <key>CFBundleName</key>
+            <string>Omega</string>
+            <key>CFBundleDisplayName</key>
+            <string>Omega</string>
+            <key>CFBundleVersion</key>
+            <string>1</string>
+            <key>CFBundleShortVersionString</key>
+            <string>1.0.0</string>
+            <key>CFBundlePackageType</key>
+            <string>APPL</string>
+            <key>LSMinimumSystemVersion</key>
+            <string>14.0</string>
+            <key>NSHighResolutionCapable</key>
+            <true/>
+            <key>com.apple.security.app-sandbox</key>
+            <false/>
+            <key>com.apple.security.network.client</key>
+            <true/>
+            <key>NSAppTransportSecurity</key>
+            <dict>
+              <key>NSAllowsArbitraryLoads</key>
+              <true/>
+            </dict>
+          </dict>
+          </plist>
+          PLIST
+
+          codesign --force --sign - OmegaMac.app
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: OmegaMac
+          path: apps/omega-mac/OmegaMac.app

apps/omega-mac/Package.swift

@@ -3,7 +3,7 @@ import PackageDescription
 
 let package = Package(
     name: "OmegaMac",
-    platforms: [.macOS(.v15)],
+    platforms: [.macOS(.v14)],
     dependencies: [
         .package(url: "https://github.com/gonzalezreal/swift-markdown-ui", from: "2.4.0"),
     ],