DonutSMP payment verifier

• Added a Fabric server-side mod that watches broadcast messages for payments to icefragged (or DONUTSMP_RECIPIENT) and logs deposits into a ledger. When a match is seen, the payer is notified in-game with their Discord link code and the event is recorded.
• Ledger persistence lives in config/donutsmp-ledger.json and tracks deposits, link codes, saved Discord IDs, and withdrawal requests so data survives restarts.
• Commands for players:
  • /deposit [amount] shows how to pay icefragged, reports recorded totals, and surfaces the current link code for the Discord bot.
  • /donutsmp linkdiscord <discordId> saves the player’s Discord identifier for webhook notifications.
  • /donutsmp linkcode (or /donutsmp linkcode refresh) displays or regenerates the link code to share with the Discord bot.
  • /withdraw <amount> opens a withdrawal request; nothing is auto-processed.
• Staff commands (permission level 2+): /withdraw pending lists queued requests, /withdraw approve <id> [note] and /withdraw deny <id> [note] move requests forward for manual payouts.
• Optional Discord webhook notifications fire for deposits and withdrawal status changes when DONUTSMP_DISCORD_WEBHOOK is set; payloads include Minecraft name, Discord ID (if linked), amount, link code, and the raw payment text.
• Default recipient is icefragged; change it via DONUTSMP_RECIPIENT to retarget detection without rebuilding.