feat(extract): multi-texture & 3D/4D texcoords + matrix/multi texture transforms

[delta9000]

What

Extends texture extraction to the multi-channel and higher-dimension texture coordinate / transform nodes, and adds reader-tolerant field aliasing. Resolves four conformance findings.

Finding	Clause	Before	After
TXT-6	§18.4.4	MultiTextureCoordinate silently fell back to default UVs (it has no point field)	MeshBuilder unwraps MultiTextureCoordinate.texCoord children into MeshData.texcoordSets (all channels preserved), mirrors the first usable channel onto the legacy MeshData.texcoords seam, emits (0,0) fallback corners for empty channels
T3D-3	§33.4.4	TextureCoordinate3D/4D point arrays were never extracted	reads MFVec3f/MFVec4f and projects onto the 2D (s,t) seam — (s,t) for 3D, homogeneous (s/w, t/w) for 4D
TXF-3	§18.4.10	only the single TextureTransform was handled	MultiTextureTransform → one TextureTransform2DParams per child, applied per-channel; TextureTransformMatrix3D projects its 4×4 over (s,t,0,1)
TPJ-2	§42.4.2	strict readers dropped the spec-erratum spelling shadowsIntensity	reader-only FieldAliases.hpp accepts it on TextureProjectorParallel as a tolerant alias for canonical shadowIntensity across XML, ClassicVRML, VRML97, JSON. Writers stay canonical

How

• MeshData gains texcoordSets (per-channel UVs); the legacy single-channel texcoords is preserved and mirrors the first usable channel, so existing consumers (PickSystem, both renderers) are unaffected on the common path.
• applyTextureTransformsToMesh / textureTransformParamsListOf are the new plural entry points; SceneExtractor switches to them. Identity transforms / absent textureTransform still early-out with no allocation.
• TextureTransform2DParams gains an optional hasMatrix path used by TextureTransformMatrix3D.
• FieldAliases.hpp (codecs) is purely reader-side: it remaps accepted input spellings to canonical field names during ingest and changes no node metadata or writer output.

Tests / gates

• texture_extract_test: multi-texture coords (incl. empty leading channel), 3D/4D projection, MultiTextureTransform, TextureTransformMatrix3D.
• reader_audit_test: shadowsIntensity alias across all four encodings.
• mise run build-ci green — 112/112 ctest. mise run conformance-gate clean (generated view matches findings.yaml).

Notes / scope

• texcoordSets is forward-looking plumbing: no renderer consumes the extra channels yet, so multi-channel UVs are extracted and transformed but only channel 0 reaches the current single-texture render path. The 3D/4D → 2D projection and matrix → 2D projection are the spec-permitted implementation-dependent fallbacks onto the current single-(s,t) seam, not full volumetric/3D-texture support.
• Independent of (and not stacked on) the GLFW examples-gate fix in fix(poc): GLFW_INCLUDE_NONE — repair the headless examples-gate (GL/gl.h) #41.