add macos ci

hopefully this works first try :3

.github/workflows/macos.yml

@@ -0,0 +1,31 @@
+name: "Build APK"
+
+on:
+  push:
+    branches: ["main"]
+    tags: ["*"]
+  workflow_dispatch:
+
+jobs:
+  build-apk:
+    runs-on: macos-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+        with:
+          submodules: recursive
+
+      - name: Lix GHA Installer Action
+        uses: samueldr/lix-gha-installer-action@v2026-02-22
+        with:
+          extra_nix_config: experimental-features = nix-command flakes flake-self-attrs
+
+      - name: Build app
+        run: nix develop --command bash -c "flutter pub get && dart scripts/generate.dart && flutter pub run build_runner build && flutter build macos --release"
+
+      - name: Upload installer artifact
+        uses: actions/upload-artifact@v6
+        with:
+          name: App
+          path: build/macos/Build/Products/Release/Nexus.app