Add configurable offline UUID modes with prefix support

[AeiouJx]

Summary

Adds configurable UUID generation modes for offline authentication.

Changes

• New OfflineUUIDMode enum: RANDOM, FIXED, GENERATED
• New config fields: offlineUUIDMode, offlineUUIDPrefix
• unsupported auth offlineUUID gains new subcommands:
  • mode <random/fixed/generated>
  • prefix <prefix> (default: OfflinePlayer:)
  • set <uuid> (also switches to FIXED mode)
  • clear (reset to RANDOM mode)

Usage

unsupported auth offlineUUID mode generated unsupported auth offlineUUID prefix OfflinePlayer: unsupported auth offlineUUID mode fixed unsupported auth offlineUUID set 123e4567-e89b-12d3-a456-426614174000

Notes

• Default mode is RANDOM (preserves existing behavior)
• GENERATED uses UUID.nameUUIDFromBytes((prefix + username).getBytes(UTF_8))
• FIXED falls back to random if no UUID configured

[rfresh2]

does not seem useful enough to be worth the complexity

but you can set Globals.CONFIG.auth.offlineUUID with whatever special logic you want from a plugin