stitchSingleModel

Generic-pipeline entry point: stitch a single in-memory Java item model into a Bedrock atlas. The model is treated as a single "bone" named boneName so the existing per-bone icon machinery still applies. Use modelName = <namespace> and boneName = <path with slashes replaced by underscores> to avoid collisions across plugins.

This was added in Phase 6 of the generic Java→Bedrock pipeline so the generic 3D path can reuse TextureStitcher's atlas building and sprite-map UV computation without having to write the resolved/merged JSON back to disk. The generic path renders a small perspective item icon separately, so this entry point intentionally does not copy full source textures into textures/items/<modelName>__<boneName>.png.

The output atlas path is textures/entity/<modelName>/<boneName>/atlas.png — per-(model x bone) scoping is required because in this pipeline modelName is the plugin namespace (e.g. "elitemobs") shared by many independent models. FMM's stitch uses textures/entity/<modelName>/atlas.png because its modelName is already unique per FMM model directory.