Add referral discount to payment preview for users with unused referral discounts.
- Check referral_discounts table for unused discounts in calculateDiscountPreview
- Wrap campaign discount application in a proper database transaction
- Apply eligibility guard for 2nd+ payments to prevent duplicate discount application
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
- Added generic formatAndPreserveCursor() helper on frontend to track
and restore selection caret position during dynamic input sanitization
- Applied to all card inputs, gift card code inputs, and expiry inputs
- Added Luhn validation (isValidLuhn) for saved cards and gift cards
- Rebuilt payments test DB and got 100% green tests
Add validators.IsValidID() checks on URL param IDs to return 404 instead of 400 for invalid IDs. Add offset cap and query length limit in portfolio images handler.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
popertotsandSisyphus