PlayerControl implementation reference

The user-supplied playercontrol-master.zip (Java package
ml.mypals.controlPlayer, mod ID fackplayercontrol) was reviewed for the
possession implementation. Its LICENSE and fabric.mod.json declare CC0-1.0.

FGA adapts the reference mod's in-memory snapshot, inventory, profile,
dimension, passenger and client-view refresh approach for the existing
`/player <name> possess` command. The adapted code is self-contained and does
not depend on PlayerControl at runtime. Player entities, UUIDs and persistent
playerdata are retained by FGA; no offline data is copied or rewritten.

The supplied archive's project metadata contains template author/source
placeholders, so no upstream author or repository URL is asserted here.
