feat(3d): gl1 shim M4+M6+M7 — GLU quadrics, production link, stub retired; 47/47 parity

- gl1_glu: gluCylinder/gluDisk/gluSphere per the SGI GLU reference
  tessellation (sin/cos phase, strip emission order, pole fans — Apple's
  GLU derives from the same source, so vertices match the goldens);
  emission goes through the public glBegin/glVertex entry points so
  quadrics record into display lists
- glLineWidth>1 one-time warning (browsers clamp to 1; affected coverage
  stays under the parity floor — zero floors.json overrides needed)
- production link site: build-kicad-target.sh now compiles wasm/gl1 from
  sources.txt and applies wrapped_symbols.txt --wrap flags (same manifests
  as the test harness); kicad_editor's RENDER_3D_OPENGL links against the
  real emulation layer instead of no-ops
- wasm/stubs/gl_ffp_stub.c deleted (role fully superseded; history in git)
- docs: 3d-regression README port-status section (floor-blind small
  geometry + line-width caveats), harness comments de-red-stated

Parity: 47/47 under the 0.02 floor, zero overrides. Native golden path
byte-identical to bb0e238 (whose gate ran green) — scenarios/, native/,
baseline/, manifest, floors, spec all untouched by the port.

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

tests/3d-regression/wasm/3d_webgl_test.cpp

@@ -1,8 +1,8 @@
 /**
  * 3D-renderer WebGL test harness (WASM) — runs the shared scenarios
- * (tests/3d-regression/scenarios/) in the browser. Today the legacy GL
- * surface is wasm/stubs/gl_ffp_stub.c no-ops, so every scenario renders a
- * black canvas: the TDD red state the WebGL port turns green.
+ * (tests/3d-regression/scenarios/) in the browser. The legacy GL surface is
+ * implemented by the wasm/gl1 GL1->WebGL2 emulation layer; the parity level
+ * (npm run 3d:check:parity) compares these renders against the native goldens.
  *
  * Unlike the GAL harness this needs no wx window: the renderer draws into
  * whatever context is current, so a direct emscripten WebGL2 context on