feat(nav): surface Data in the primary app menu (IMP-IA-01)

Import/export/backups (/data) was only reachable from the account overflow
dropdown + command palette — buried for how central it is. Move it into the
main Tracker nav menu alongside Bills/Categories/Spending/… so it appears in
both the desktop dropdown and the mobile nav.

Preserves the existing gate: Data stays hidden for the default-admin account
(new `accountToolsOnly` flag on the nav item, filtered by the same
`!user.is_default_admin` check the account dropdown used). Removed the now
-redundant account-dropdown entry; command palette entry unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/components/layout/Sidebar.jsx

@@ -46,6 +46,7 @@ const trackerItems = [
   { to: '/bank-transactions', icon: Landmark, label: 'Banking', simplefinOnly: true },
   { to: '/snowball', icon: TrendingDown, label: 'Snowball' },
   { to: '/payoff',   icon: Calculator,  label: 'Payoff' },
+  { to: '/data', icon: Database, label: 'Data', accountToolsOnly: true },
 ];
 
 function TrackerMenu({ onNavigate, badge, badgeNames = [], items = trackerItems }) {
@@ -164,10 +165,6 @@ function UserMenu({ adminMode = false }) {
               <Settings className="h-4 w-4" />
               Settings
             </DropdownMenuItem>
-            <DropdownMenuItem onSelect={() => navigate('/data')}>
-              <Database className="h-4 w-4" />
-              Data
-            </DropdownMenuItem>
             <DropdownMenuSeparator />
           </>
         )}
@@ -199,9 +196,13 @@ export default function Sidebar({ adminMode = false }) {
   const { data: overdueData } = useOverdueCount();
   const overdueCount = (!adminMode && overdueData?.count) ? overdueData.count : 0;
   const overdueNames = (!adminMode && overdueData?.names) ? overdueData.names : [];
+  const accountToolsAllowed = !user?.is_default_admin;
   const trackerMenuItems = useMemo(
-    () => trackerItems.filter(item => !item.simplefinOnly || simplefinReady),
-    [simplefinReady],
+    () => trackerItems.filter(item => (
+      (!item.simplefinOnly || simplefinReady)
+      && (!item.accountToolsOnly || accountToolsAllowed)
+    )),
+    [simplefinReady, accountToolsAllowed],
   );
 
   useEffect(() => {