Implement business loan repayment system

[PipFoweraker]

Summary

Business loans are currently disabled ('Coming Soon') because they require a repayment system.

Requirements

1. Debt tracking - GameState needs a 'debt' field
2. Repayment schedule - X% of money per turn goes to loan repayment
3. Default consequences - What happens if you can't pay?
   • Increased doom?
   • Reputation damage?
   • Forced asset seizure?
4. Multiple loans - Can you take multiple loans? Interest stacking?

Current State

• Action exists in get_fundraising_options() with is_stub: true
• Execution handler returns 'Coming Soon' message
• Gains defined as money: 75000, debt: 90000 (15k interest)

Related

This is part of making the financial gameplay more strategic and realistic.