GH-129 Use PaperItemBuilder in leaderboard menu to fix crash on modern Paper (#129)

The leaderboard menu used triumph-gui's Bukkit ItemBuilder, which serializes item names/lore through adventure-platform's MinecraftComponentSerializer. The bundled adventure-platform is built against an older adventure-api and fails on servers whose bundled Adventure no longer has ComponentFlattener.toBuilder(), crashing the menu render:

java.lang.UnsupportedOperationException: java.lang.NoClassDefFoundError: Could not initialize class net.kyori.adventure.platform.bukkit.BukkitComponentSerializer Caused by: java.lang.NoSuchMethodError: 'net.kyori.adventure.util.Buildable$Builder net.kyori.adventure.text.flattener.ComponentFlattener.toBuilder()'

Since EternalEconomy is a Paper plugin, switch to the triumph-gui-paper artifact and PaperItemBuilder, which set name/lore via Paper's native Component API (ItemMeta#displayName/#lore) and avoid the reflective serializer entirely.

Co-authored-by: Claude Fable 5 [email protected]