Player gets its own CapsuleShape3D (was a small CylinderShape3D, never
actually shared with anything — the shared oversized capsule flagged
earlier only affects the 4 mountain props, unrelated to the player).
Real cause of the fall-through: the crown collision is a zero-thickness
trimesh and the player spawned with exactly zero clearance sitting
right on the surface, a classic tunneling setup. Fixed by giving the
trimesh backface_collision (collide from both sides) and spawning the
player with a bit of headroom so it settles onto the floor instead of
starting embedded in it. Verified headless: player now falls from
spawn height to rest exactly on the surface and stays on_floor=true
over a 3s simulated run.
Promote debug/HexDiamondIsland.gd to terrain.gd at project root now
that main.tscn depends on it, and swap it in for the old flat
checkerboard Ground (Player/Camera/POI untouched, table sits at the
same y=0 the old ground surface used).
Add _build_region_borders(): places mountain.glb/mountain2v5.glb/
forest.glb (same models, scale factors and hitbox sizes already used
elsewhere in main.tscn) continuously along the 6 ridges between table
corners and girdle corners, i.e. the shared edges between adjacent
outer regions.
