Bake and embed textures from layer stack into GLB export

**Feature description:**
Add the ability to bake and embed textures from the layer stack into GLB export. Currently, meshes can be exported to GLB format, but the textures are not included in the export. The feature should apply all layers from the layer stack (similar to Blender's bake functionality) and embed the resulting textures into the GLB file.

This is different from issue #2008 which focuses on exporting texture paths. This request is about actually baking and embedding the textures into the GLB file.

**Why this is needed:**
- GLB files without materials/textures are limited in use
- Current knife export works but lacks textures
- Having baked materials in GLB would make the exported models immediately usable in other applications
- Similar to how Blender handles texture baking for GLB export

**Proposed implementation:**
- Add a checkbox or option in the GLB export dialog: "Bake and embed textures"
- When enabled, bake all layers from the layer stack onto the mesh
- Embed the resulting textures into the GLB file
- This would be similar to the existing bake functionality but specifically for GLB export

Start with the GLB export dialog and the existing bake functionality referenced in the issue. Determine how the export option should trigger baking all layer-stack layers and embed the resulting textures; done means an enabled option produces a GLB with baked materials and embedded textures, while the existing export behavior remains available.

Written by the indexing model from the issue text.