BU engineering-review mesh source notices

BU derives from the six saved BT native files.  It removes the inherited
0.2 mm-high circular upper-housing platform around the right six-point star;
the surrounding upper surface is flat at local z=20.0 mm.  The BT star metal,
central hexagonal optic, left lamp, boards, fasteners, ordinary-Topre plate and
BR lower-shell relief are preserved.

This non-commercial review contains tessellated display assets, not fabrication
files or a manufacturing release. Native CAD, KiCad, STEP and Gerber files are
not included. Segmented-metal fabrication, adhesion, optical uniformity,
tolerances, supplier DFM and real assembly remain unapproved.

EC60 main-board body basis
Source: https://github.com/4pplet/EC60
Commit: b9c04625bb9944f6fb806aa571da8592cdff8565
Copyright (c) 2022 Cipulot. MIT License; see EC60-LICENSE.txt.

Topre plate and ai03 UDB-C4 notices are retained in the adjacent license files.
All source components and adaptations are provided without warranties.