Added auto-generated "Updated..." line under H1 (#719)

scripts/git-dates.mjs

@@ -0,0 +1,18 @@
+import { execSync } from 'child_process'
+
+/**
+ * Get the last modified date for a file from git history.
+ * Returns YYYY-MM-DD or null if the file is not tracked / git is unavailable.
+ */
+export function getGitLastModified(filePath) {
+  try {
+    const date = execSync(`git log -1 --format=%cI -- "${filePath}"`, {
+      encoding: 'utf-8',
+      stdio: ['pipe', 'pipe', 'ignore'],
+    }).trim()
+
+    return date ? date.split('T')[0] : null
+  } catch {
+    return null
+  }
+}