Move the signed-in-as/sign-out block to the bottom of the sidebar

Was a separate top page-header bar above every page's content. Moved
into the vertical navbar itself using Tabler's own .navbar-footer
class (order:1 + margin-top:auto), which pins it to the bottom of the
sidebar regardless of how many nav items are above it. Removed the
now-empty page-header entirely.

Verified visually in the browser at both desktop width (sidebar is
position:fixed there — footer sits flush at the bottom) and mobile
width (collapsed dropdown menu — footer just follows the nav list).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/layout/AppShell.tsx

@@ -72,28 +72,19 @@ export default function AppShell({ user, children }: { user: CurrentUser; childr
                 </li>
               ))}
             </ul>
-          </div>
-        </div>
-      </aside>
-
-      <div className="page-wrapper">
-        <div className="page-header d-print-none">
-          <div className="container-xl">
-            <div className="row g-2 align-items-center">
-              <div className="col">
-                <span className="text-secondary">
+            <div className="navbar-footer px-3">
+              <div className="text-secondary small mb-2">
                 Signed in as {user.name ?? user.email ?? user.sub} · {user.role}
-                </span>
               </div>
-              <div className="col-auto ms-auto d-print-none">
-                <a className="btn btn-outline-secondary btn-sm" href="/auth/logout">
+              <a className="btn btn-outline-secondary btn-sm w-100" href="/auth/logout">
                 Sign out
               </a>
             </div>
           </div>
         </div>
-        </div>
+      </aside>
 
+      <div className="page-wrapper">
         <div className="page-body">
           <div className="container-xl">{children}</div>
         </div>