add github tooling

.github/dependabot.yml

@@ -0,0 +1,7 @@
+version: 2
+
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: monthly

.github/workflows/ci.yml

@@ -0,0 +1,27 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.ref }}
+
+      - uses: DeterminateSystems/flake-checker-action@v7
+
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+
+      - run: nix develop -c prettier -w .
+      - run: nix fmt .
+      - uses: EndBug/add-and-commit@v9
+        with:
+          message: "chore: lint"
+          default_author: github_actions