NPC marchant

NPC Merchant adds a creative-only spawn egg that places a living villager-style 
merchant NPC. Each merchant is fully configurable in-game and integrates with 
Lightman's Currency for payments.

## Features

**The merchant**
- Spawn it with a creative-only egg (moderators only)
- A living, named villager-style NPC that can't be pushed, damaged, or despawn
- Custom blue/white Pokémon-vendor texture

**For customers** (right-click with empty hand or any item)
- A dialogue opens: "Hello! Buy or sell?"
- **Buy** → browse the items the merchant sells (2-column scrollable list)
- **Sell** → drop an item in the deposit slot to see how much the merchant pays, then confirm

**For owners/moderators** (right-click with the spawn egg)
- Pick any item from a searchable grid of ALL modpack items
- Set the price and which coin tier it costs (copper → netherite)
- Choose whether the NPC sells or buys each offer (up to 9 offers)
- Rename the merchant and withdraw collected coins

**Money integration**
- Uses Lightman's Currency coins (copper, iron, gold, emerald, diamond, netherite)
- Robust integration: references the coin items directly, so it never breaks on Lightman's updates

## Commands
- Get the egg: /give @s npcmerchant:merchant_spawn_egg

## Requirements
- NeoForge 21.1.216+
- Lightman's Currency (recommended, provides the coins)