PvP event starting

PvP event starting plugin drops everyone into a Hunger Games-style ring around the world spawn, freezes them, and lets an operator trigger a 10-second release countdown.

• Command: /pvpevent prepare teleports all online players to evenly spaced spots on a circle around the main world spawn, faces them toward center, and locks their movement.
• Command: /pvpevent release starts the 10-second countdown; when it ends, movement is unlocked and players are notified.
• Permission: pvpeventstarting.manage (defaults to operators) gates both subcommands.
• Preparing again clears any existing freeze list and countdown before re-placing players.
• Movement lock stops position changes but still allows players to look around.

Limitations/suggestions: Newly joining players after preparation are not auto-frozen; rerun /pvpevent prepare if you need them included. Radius is dynamic but fixed per run—change the code if you want it configurable.