Реализовать систему торговли между NPC и игроком

# Trading System for RPG

Merchant System

Complete trading system with merchant inventory, buy/sell mechanics, dynamic pricing, and reputation system.

Core Components

MerchantInventory - Manages merchant stock with separate buy and sell prices. Supports limited money pool and automatic restocking.

MerchantManager - Handles buy/sell transactions with price calculations, reputation tracking, and discount application.

TradeItem - Data structure with item reference, quantity, buy price, and sell price.

ShopUI - User interface for browsing items, selecting quantities, and confirming transactions.

Features

• Merchant inventory with independent buy/sell prices
• Limited merchant money pool (prevents exploitation)
• Reputation system with dynamic discounts (±5%)
• Auto-restocking every 60 seconds
• Transaction confirmation dialog
• Full buy/sell support from both directions

Bonuses Implemented

• Reputation-based discounts: good reputation = lower prices (up to 5% discount)
• Merchant stock replenishment with time-based intervals
• Friendship tracking per merchant with persistent reputation

Architecture

Event-driven system with loose coupling between components. Price calculations apply reputation modifier. Money management prevents merchant bankruptcy.