ci: add workflows for building the minimal flake

closes GH-10

.github/dependabot.yml

@@ -0,0 +1,8 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    commit-message:
+      prefix: "ci"

.github/workflows/build.yml

@@ -0,0 +1,31 @@
+name: Build
+
+on:
+  push:
+    branches: [develop, main]
+  pull_request:
+    branches: [develop, main]
+  workflow_dispatch:
+
+jobs:
+  flake-health-check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Check flake health
+        uses: DeterminateSystems/flake-checker-action@v9
+
+  build:
+    runs-on: ubuntu-latest
+    needs: flake-health-check
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@v14
+      - name: Run the Magic Nix Cache
+        uses: DeterminateSystems/magic-nix-cache-action@v8
+      - name: Run Nix flake checks
+        run: |
+          nix flake check

.github/workflows/update-flake-lock.yml

@@ -0,0 +1,33 @@
+name: Update flake.lock
+
+on:
+  schedule:
+    - cron: "0 0 * * 0"
+  workflow_dispatch:
+
+jobs:
+  lockfile:
+    name: Run update
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: write
+      pull-requests: write
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@v14
+      - name: Run the Magic Nix Cache
+        uses: DeterminateSystems/magic-nix-cache-action@v8
+      - name: Check flake health
+        uses: DeterminateSystems/flake-checker-action@v9
+      - name: Update flake.lock
+        uses: DeterminateSystems/update-flake-lock@v24
+        with:
+          commit-msg: "build(nix): update flake.lock"
+          pr-assignees: 21CSM
+          pr-reviewers: 21CSM
+          pr-title: "Update flake.lock"
+