fix: chat UI fixes

app/layout.tsx

@@ -1,4 +1,4 @@
-import type { Metadata } from "next";
+import type { Metadata, Viewport } from "next";
 import Script from "next/script";
 import { Geist, Geist_Mono, Lora, Bricolage_Grotesque } from "next/font/google";
 import { ogDefault } from "@/lib/og";
@@ -43,6 +43,16 @@ const bricolage = Bricolage_Grotesque({
   display: "swap",
 });
 
+export const viewport: Viewport = {
+  width: "device-width",
+  initialScale: 1,
+  // Ask the browser to shrink the layout viewport when the software keyboard
+  // opens, which is the native fix for a bottom-anchored composer. Chrome and
+  // Android honour it; Safari does not, which is why the chat thread also
+  // tracks window.visualViewport by hand.
+  interactiveWidget: "resizes-content",
+};
+
 export const metadata: Metadata = {
   // Resolves all relative OG/Twitter image URLs and canonical links to
   // absolute URLs (required for correct social previews + SEO; Next warns