docs: rewrite docs site pages to be shorter and easier to scan

- Pages now start with setup and usage, and reference material is in compact tables
- Configuration reference gives each config block a short explanation and a key/default table
- Internal detail removed from user pages, and docs that had drifted from current behavior fixed
- The status line shows today's date, set on the client, instead of the page's last-updated date
- Add changelog fragment

docs-site/.vitepress/theme/status-line.ts

@@ -2,3 +2,10 @@ export function formatStatusLineFilePath(routePath: string): string {
   if (routePath === '/') return 'index.md';
   return `${routePath.replace(/^\/|\/$/g, '')}.md`;
 }
+
+// Local calendar date as YYYY-MM-DD (toISOString would give the UTC date).
+export function formatStatusLineDate(date: Date): string {
+  const month = String(date.getMonth() + 1).padStart(2, '0');
+  const day = String(date.getDate()).padStart(2, '0');
+  return `${date.getFullYear()}-${month}-${day}`;
+}