fix: nav buttons now navigate, not just toggle store state

The [S] button only called setDM(false) without navigating away from
/chat area. Since the notes-to-self feature now calls navigate('/dm/:id'),
the URL stayed at /dm/... and ChatArea never re-mounted.

[S] now navigates to /, [@] navigates to /dm.

web/src/components/Layout.tsx

@@ -120,7 +120,7 @@ export function Layout() {
         <div className="flex-1 flex min-h-0">
           <div className="flex flex-col items-center w-16 bg-gb-bg-h border-r border-gb-bg-t py-2 gap-2 shrink-0">
             <button
-              onClick={() => setDM(false)}
+              onClick={() => { setDM(false); navigate('/'); }}
               className={`w-11 h-11 flex items-center justify-center font-mono text-xs border rounded ${
                 !isDM
                   ? 'bg-gb-bg-t text-gb-orange border-gb-orange'
@@ -134,6 +134,7 @@ export function Layout() {
               onClick={() => {
                 setDM(true);
                 setActiveServer(null);
+                navigate('/dm');
               }}
               className={`w-11 h-11 flex items-center justify-center font-mono text-xs border rounded ${
                 isDM