Add GitHub Actions CI workflow

- CI: Build on push/PR to main (macOS 14, Swift 5.9, debug + release)
- Notarization workflow deferred until Apple Developer account is available

Author: RAKKUNN

.github/workflows/ci.yml

@@ -0,0 +1,33 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    name: Build & Test
+    runs-on: macos-14
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Swift
+        uses: swift-actions/setup-swift@v2
+        with:
+          swift-version: "5.9"
+
+      - name: Resolve dependencies
+        run: swift package resolve
+
+      - name: Build (Debug)
+        run: swift build -c debug
+
+      - name: Build (Release)
+        run: swift build -c release