fix: add feedback after successfully adding a user in admin panel

[bimakw]

Summary

• Show success toast notification after user is added
• Refresh user list and navigate to 'normal' filter on page 1 to display the newly added user

Problem

When adding a user in Admin -> Users, the page had no feedback after submission (as reported in #1457).

Root cause: The code only refreshed the user list if the current filter was "all" or "staff", but the default filter is "normal". Additionally, there was no success toast notification.

Solution

1. Added toast notification to confirm successful user creation
2. After adding user, navigate to "normal" filter page 1 and refresh the list so the new user is visible

Test plan

1. Go to Admin -> Users
2. Click "Add User"
3. Submit user information
4. ✅ Success toast should appear
5. ✅ Page should navigate to "normal" filter
6. ✅ Newly added user should be visible in the list

Fixes #1457

[shuashuai]

Great, thanks for the contribution！