Add persistent navbar with SSH Keys link

Refactor App.tsx to use Layout + Outlet pattern with sticky navbar
containing: Dashboard | Machines | Sync Pairs | Jobs | SSH Keys | Settings.
Clean up redundant button row from Dashboard and inline SSH Keys links.

web/src/pages/Dashboard.tsx

@@ -1,5 +1,4 @@
 import { useEffect, useState } from 'react';
-import { Link } from 'react-router-dom';
 import { api, Machine, Job } from '../api/client';
 
 export default function Dashboard() {
@@ -66,11 +65,6 @@ export default function Dashboard() {
           </table>
         )}
       </div>
-      <div className="mt-4 flex gap-4">
-        <Link to="/machines" className="bg-blue-600 hover:bg-blue-700 text-white px-4 py-2 rounded">Machines</Link>
-        <Link to="/sync-pairs" className="bg-blue-600 hover:bg-blue-700 text-white px-4 py-2 rounded">Sync Pairs</Link>
-        <Link to="/jobs" className="bg-blue-600 hover:bg-blue-700 text-white px-4 py-2 rounded">All Jobs</Link>
-      </div>
     </div>
   );
 }