test(3d): screenshot-baseline TDD suite for the 3D viewer OpenGL->WebGL port — 47 native goldens + red-state WebGL harness

tests/3d-regression mirrors the gal-regression pattern at renderer scale:
shared C++ scenarios call real KiCad 3D-viewer code (opengl_utils, display
lists + DrawCulled stencil subtraction, MODEL_3D VBOs, private generators via
a rob-template accessor, and full reload()+Redraw() composites over a
synthetic BOARD_ADAPTER). A native macOS harness renders them on real OpenGL
into 47 committed goldens (bit-deterministic, FBO capture); the wasm harness
compiles the same TUs against wasm/stubs/gl_ffp_stub.c no-ops so every
scenario renders blank — the TDD red state (parity meter: 47/47 changed).
Comparisons use the CI pixelmatch engine via the new generic compare-dirs.ts
(floors.json levels; manifest.json cmp-guards registry drift).

Documents an upstream bug: appendPostMachiningGeometry's countersink path
adds middle quads without normals, silently erasing the walls of any
display list it is batched into (3d-post-machining.png keeps the lists
separate to record it).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -65,6 +65,8 @@ wxwidgets-clean/
 !tests/apps/kicad/pcbnew.html
 /tests/apps/gal-webgl/*.js
 /tests/apps/gal-webgl/*.wasm
+/tests/apps/3d-webgl/*.js
+/tests/apps/3d-webgl/*.wasm
 /temp/
 *.log
 *.tmp