Portable homes

• Added a Portable Home Block item that links to a player's own pocket-dimension plot. Use the item in hand or interact with a placed block (sneak+use also works) to warp; first use builds a small landing pad and drops an anchor block there.
• Every player receives a bound block on join if they do not already have one; on death a bound block is dropped so others can pick it up and visit that base.
• Portable home blocks cannot live in ender chests—if placed there they are ejected and dropped at the player's feet each server tick.
• The pocket world is a flat, calm overworld-themed dimension with daylight locked; each player is assigned a unique, widely spaced platform to build on.
• Breaking the anchor block drops a bound item carrying the same owner data so bases remain accessible; teleporting also sets the player's spawn in their pocket.

Known notes/limits:

• Explosions will not drop the anchor item; keep a spare block item if creepers are common.
• Players who lose their key receive a new one on next join to avoid being stranded, which means old keys can still exist in the world.