FloatPet: floating (no-gravity) pet class

Idea

A separate pet class for floating creatures (ghost, orb, slime-in-air, etc.) that aren't affected by gravity — they drift and bob in 2D rather than walking on the floor.

Rough shape discussed (NOT finalized — brainstorm deferred):

• Idle = gentle vertical bob/hover, never rests on the ground.
• Drift (its wander) = pick a random 2D point and float there; follow/dash/play in 2D.
• No gravity, no jump; dragged = stays where dropped, resumes drifting.
• Its own config action set (flicker/spin/phase instead of nap/groom).
• Code org: extract shared brain into a base PetBrain; GroundPet + FloatPet as thin subclasses differing only in locomotion.

Status

Deferred — the user has a more specific/complex vision for floating pets. Brainstorm this properly (its own spec) before building. The ground-pet personality/behavior work (retreat, zoomies, play, jiggle_reaction, personality presets) lands first and establishes the shared engine that FloatPet will subclass.