feat: add account navigation and footer

Move Inbox into a top-right account area, add a profile page for the authenticated user, and introduce a configurable sitemap and useful-links footer.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/src/components/layout/WorkspaceUtilities.tsx

@@ -0,0 +1,21 @@
+import { Inbox } from 'lucide-react'
+import { NavLink } from 'react-router-dom'
+import type { User } from '../../types'
+
+export function WorkspaceUtilities({ user }: { user: User | null }) {
+  const profileLabel = user?.displayName || user?.email || 'Profile'
+  return (
+    <nav className="workspace-utilities" aria-label="Account navigation">
+      <NavLink className="utility-link" to="/inbox">
+        <Inbox size={18} aria-hidden="true" />
+        <span>Inbox</span>
+      </NavLink>
+      <NavLink className="utility-link profile-utility" to="/profile">
+        <span className="avatar tiny" aria-hidden="true">
+          {profileLabel.slice(0, 2).toUpperCase()}
+        </span>
+        <span>{profileLabel}</span>
+      </NavLink>
+    </nav>
+  )
+}