feat: add CI workflow to check flake

.github/workflows/check-flake.yml

@@ -0,0 +1,23 @@
+name: Check Nix Flake
+on:
+  push:
+  pull_request:
+permissions:
+  contents: read
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+jobs:
+  flake-check:
+    name: Check Nix Flake
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+      - name: Setup Nix Cache
+        uses: DeterminateSystems/magic-nix-cache-action@main
+      - name: Check Nix Flake
+        shell: bash
+        run: nix flake check