- Update user creation logic to strip 'user_' prefix from Clerk ID before generating username
- Change default username pattern from 'user_<clerkId>' to 'user<cleanId>'
- This prevents usernames like 'user_user_35Z...' and creates 'user35Z...' instead
- Apply fix to both userService and reportController
- Add migration script to fix existing duplicate usernames
Example: user_user_35ZFZ... -> user35ZFZ...
