Fix mirrored 3D plot meshes

[shanedertrain]

Fix mirrored 3D plot meshes

The web and phone 3D viewers show reflected geometry compared with KiCad because the shared mesh encoder swaps glTF Y and Z without preserving handedness. Rotate Y-up coordinates to Z-up as (x, -z, y), preserving asymmetric landmark positions and triangle winding. Apply the same conversion to mesh bounds.

Add regression coverage that decodes the encoded mesh and checks asymmetric positions, upward-facing winding, rotated bounds, and signed underside coordinates. Update the existing serialized mesh expectation.

Validation:

• scripts/test.sh: all 91 test programs passed.
• scripts/check.sh: all type checks and formal proofs passed.
• Native build and execution of solid_orientation_test.bend: all four checks passed.
• test/tools/orbit_test.ts: all camera and wheel checks passed.
• Chromium verification using a real Bend-produced CBOR packet and src/web/solid.js: GPU positions and +Z normals matched the expected rotation.

This PR contains only the mesh conversion and its regression tests.

Fixes #45