🛒 Customer Shopping Overhaul

- Customers now search for specific products on their shopping list instead of randomly browsing shelves.

- Customers only leave the store if none of their desired products are in stock.

- Partial orders: if some products are missing, customers still check out with what they found (reduced XP & reputation)

- Missing product indicator: sad emoji + product icon appears above customers who couldn't find an item.

- Fixed: customers no longer leave with unpaid products when the checkout queue is full — they now wait and retry.

🛒 Fixed: Checkout now properly resumes where you left off

- Leaving and returning to the checkout counter mid-transaction no longer resets the state, fixing issues with payment items becoming unclickable

🚪 Fixed: Customers no longer block each other at doorways

💳 Fixed: Fixed an issue when player exits checkout during payment

Upcoming:
- UI improvements
- Customer Variants
- Employees