feat(ci): validate job

ensure that we run `make validate`
in our continuous integration,
so that any deviation from our
standards is automatically caught

.github/workflows/validate.yml

@@ -0,0 +1,19 @@
+name: Validate
+on: [push]
+
+permissions:
+  contents: read # to fetch code (actions/checkout)
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+        - uses: actions/checkout@v4
+
+        - run: corepack enable
+        - uses: actions/setup-node@v4
+          with:
+            node-version-file: '.nvmrc'
+            cache: yarn
+
+        - run: make validate