fix: export user signal from userStore.tsx

- Add user and isLoading to exports in userStore.tsx
- Enables Navbar and PanelLayout to import and use Signals store
- Fixes "does not provide an export named 'user'" error

✅ Resolves: Import error for user signal

dashboard-fresh/lib/userStore.tsx

@@ -373,6 +373,10 @@ export const useMailStore = (selector?: (state: MailState) => any) => {
 
 // Export individual mail store exports
 export {
+  // User signals
+  user,
+  isLoading,
+  // Mail signals
   mailTenantId,
   mailSelectedMessageId,
   mailLabel,