feat: MenuNav layer for the SummerCMS menu API

- typed client and useMenu/useMenuApi (SSR, menu:<code>:<locale> key,
  server and public bases, x-forwarded-for forwarded also on cached renders)
- MenuNav and recursive MenuNavItem: WAI disclosure navigation, URL
  allowlist with a text fallback, rel on _blank, active link and trail,
  mobile toggle, Esc / focus-out / outside pointer / route change closing
- menu tokens and base CSS, README
- node tests (link rules, client, server-rendered NavItem) and a playground
  SSR smoke against a fixture API

server/plugins/menu-client-address.ts

@@ -0,0 +1,17 @@
+// Keeps the visitor's address available to route-cached SSR renders.
+//
+// An app rule such as `'/**': { swr }` renders cached pages from a copy of
+// the request without headers. The menu API throttles per client address,
+// so forwarding only the Nuxt peer would put every cache miss in one bucket.
+// The event context is shared with that copy, so the incoming
+// x-forwarded-for plus the peer address is recorded here, before the cached
+// handler runs, and useMenuApi forwards it.
+
+export default defineNitroPlugin((nitroApp) => {
+  nitroApp.hooks.hook('request', (event) => {
+    const forwarded = [getRequestHeader(event, 'x-forwarded-for'), event.node.req.socket?.remoteAddress]
+      .filter((v): v is string => typeof v === 'string' && v !== '')
+      .join(', ')
+    event.context.menuForwardedFor = forwarded
+  })
+})