AI: meshoptimizer-backed LOD generation

[fernandotonon]

Parent epic: #397

Goal

Replace/augment the current Ogre-based LOD chain in qtmesh lod with meshoptimizer's simplify + simplifyAttr for higher-quality LODs that preserve UV seams and bone weights.

Why

The current LOD pipeline relies on Ogre's built-in MeshLodGenerator, which produces visible seam artifacts and ignores skinning attributes. meshoptimizer (MIT, ~200 KB) is the de-facto industry standard (used by glTF tooling, Godot, Unity import). Drop-in CMake dep, no ML, no model files.

Scope

• Add meshoptimizer as a CMake dependency (FetchContent or vendored).
• Implement an alternate LOD backend selectable via --algo meshopt|ogre (default: meshopt once validated).
• Preserve UV seams via simplifyWithAttributes (UV0 + bone weights as attribute streams).
• Run optimizeVertexCache on each generated LOD.
• Keep current --auto, --count N, --reductions a,b,c, --info, --remove flags fully working.
• GUI: surface as a backend dropdown in the LOD section of the inspector.
• MCP: add algo param to existing LOD tool.

Acceptance Criteria

• qtmesh lod model.fbx --count 3 --algo meshopt -o out.fbx produces three LODs with preserved UVs.
• Skinned meshes keep their bone weights through decimation.
• --info --json reports the algorithm used.
• Unit test verifies decimated triangle counts and that UV seam vertices are not collapsed.
• Sentry breadcrumb ai.assist.lod recorded.

Effort

~2–3 days.