Fix: Use nix flake check for hooks, simplify module, remove apps

.github/workflows/flake-check.yaml

@@ -0,0 +1,21 @@
+name: "Nix flake check"
+on:
+  workflow_call:
+  pull_request:
+  push:
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: cachix/install-nix-action@v31
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - name: Check formatting with nixfmt
+        run: nix run nixpkgs#nixfmt-rfc-style --check .
+      - name: Lint with statix
+        run: nix run nixpkgs#statix check
+      - name: Find dead code with deadnix
+        run: nix run nixpkgs#deadnix
+      - name: Run flake check
+        run: nix flake check --accept-flake-config