Pocket Backpack!

## 1.0.3 - first public release
- One item: right-click (or press P, rebindable) to step into your pocket from anywhere; use it again inside to come back out where you stood.
- Follows Pocket Door's rules: team and friend pockets via /pocket use, locks and bans, pets and mounts, the Hub.
- Entering starts a 60 s cooldown (survives relogs and deaths); leaving is free. 10 s combat lock after taking or dealing damage. Creative skips both.
- Pack config (config/pocketbackpack.cfg): cooldown and whether leaving counts, opening delay a hit interrupts, combat lock, fuel item per trip, dimension blacklist, in-only / out-only, sneak-to-use, key on/off.
- No Curios/Baubles slot on this version: the backpack works from your inventory.
- Requires Pocket Door 1.9.1+.