fix: forward the visitor address on route-cached renders

Nitro's cached handler renders from a header-less copy of the request, so
under swr route rules useJournalApi, /rss.xml and the sitemap source
forwarded only the Nuxt peer and every cache miss shared one Journal API
rate-limit bucket (deferred in Phase 16). A Nitro plugin records
x-forwarded-for plus the peer in event.context.journalForwardedFor on the
request hook; the three callers forward it. Same key as the host app's
workaround, which keeps working. The acme SSR smoke's x-forwarded-for check
on the now route-cached playground is the test.

server/plugins/journal-client-address.ts

@@ -0,0 +1,20 @@
+// Keeps the visitor's address available to route-cached SSR renders.
+//
+// An app rule such as `'/**': { swr }` wraps the page renderer (and any
+// matching server route) in Nitro's cached handler, which renders from a copy
+// of the request that carries no headers (only `varies` headers survive, so a
+// cached page never depends on one visitor's request). Reading
+// x-forwarded-for there would forward only the Nuxt peer, and every cache
+// miss would share the Journal API's rate-limit bucket. The event context is
+// shared with that copy, so the incoming x-forwarded-for plus the peer
+// address is recorded on the request hook, before the cached handler runs;
+// useJournalApi, /rss.xml and the sitemap source forward 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.journalForwardedFor = forwarded
+  })
+})