- Add hub.ui as main entry with stat cards (total/used/available/usage%)
- Add credit_overview.ui for user's own credit visualization with progress bars
- Add credit_manage.ui for distributor sales to manage customer credits
- Add set_credit_form.ui and set_customer_credit.dspy for credit adjustment
- Add credit_summary.dspy API for stats data
- Enhance creditlimit.py with get_credit_stats, get_my_credit_list, get_all_customer_credits
- Register new functions in init.py with ServerEnv
