add shared navbar on /account, /chat, /bee

Three-link nav (Chat / Account / Bee) with active-route highlighting,
plus a t4t Gateway home link on the left. Replaces the bespoke header
on the chat page; account and bee gain the same top-of-page nav.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/routes/account.tsx

@@ -1,4 +1,5 @@
 import { useEffect, useState } from 'react';
+import { Nav } from '~/components/nav';
 
 const API_URL = import.meta.env.VITE_API_URL ?? 'https://api.t4t-gateway.com';
 const WEI_PER_XBZZ = 10n ** 18n;
@@ -168,14 +169,19 @@ export default function Account() {
 
   if (loading) {
     return (
-      <main className='flex min-h-screen items-center justify-center'>
-        <p className='text-sm text-neutral-600'>Loading…</p>
-      </main>
+      <>
+        <Nav />
+        <main className='flex min-h-[60vh] items-center justify-center'>
+          <p className='text-sm text-neutral-600'>Loading…</p>
+        </main>
+      </>
     );
   }
 
   return (
-    <main className='mx-auto min-h-screen max-w-3xl px-6 py-12'>
+    <>
+      <Nav />
+      <main className='mx-auto max-w-3xl px-6 py-10'>
       <div className='flex items-center justify-between'>
         <div>
           <h1 className='text-2xl font-semibold'>Account</h1>
@@ -394,5 +400,6 @@ export default function Account() {
         </div>
       )}
     </main>
+    </>
   );
 }