Feat: Nix Flake install method with ci (#146)

.github/workflows/nix.yml

@@ -0,0 +1,38 @@
+name: Nix
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  id-token: write
+
+concurrency:
+  group: nix-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: DeterminateSystems/nix-installer-action@main
+
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+
+      - name: Build package
+        run: nix build .#default --print-build-logs
+
+      - name: Flake check
+        run: nix flake check --print-build-logs
+
+      - name: Verify outputs
+        run: |
+          test -x ./result/bin/emerald-legacy-launcher
+          nix path-info -Sh ./result
+          ls -la ./result/bin/
+          ls -la ./result/share/applications/ || true