Add Built-in Dynamic Pricing System

Dynamic Pricing:
- Added built-in supply/demand pricing system that works out of the box
- Prices increase when items are bought (supply decreases)
- Prices decrease when items are sold (supply increases)
- Prices gradually normalize back to base values over time
- External plugins can still override via DynamicPriceProvider API

Configuration:
- Created dynamicpricing.yml for all dynamic pricing settings
- Simplified config.yml to just dynamic-pricing: true/false
- Added per-item dynamic: false config key to exempt specific items

Admin Commands:
- /gs market status - View dynamic pricing system status
- /gs market info <item> - Check an item's current market status
- /gs market reset <item> - Reset an item to base price
- /gs market resetall - Reset all items to base prices
- Added tab completion for all market commands

Help and Tab Completion:
- Added eco and market commands to /gs help output
- Added tab completion for /gs market subcommands
- Added material name suggestions for /gs market info/reset

Documentation:
- Created wiki/Dynamic-Pricing.md with full documentation
- Updated wiki/Commands-and-Permissions.md with market commands
- Updated wiki/API-Documentation.md with Dynamic Pricing API
- Updated spigot.bbcode, modrinth.md, and dev-bukkit.html

Technical:
- Added DynamicPricingManager class with SQLite persistence
- Added shouldUseDynamicPricing() convenience method on Item
- Data stored in plugins/GUIShop/Data/dynamic_pricing.db
- Added dynamicpricing.yml to pom.xml resources