ci: add verification workflow

Per-repo content checks (JSON validity / markdown lint / Astro build /
example syntax + Go build) on push and PR.

Author: teovl

.github/workflows/ci.yml

@@ -0,0 +1,27 @@
+name: ci
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  markdown:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: List markdown files
+        run: |
+          find . -name '*.md' -not -path './.git/*' | xargs -r ls -la
+          echo "$(find . -name '*.md' -not -path './.git/*' | wc -l) markdown files"
+
+      - name: Lint markdown (advisory)
+        uses: DavidAnson/markdownlint-cli2-action@v16
+        continue-on-error: true
+        with:
+          globs: '**/*.md'