Blender: one shared headless runner, delete the seven copies #3821

The same Blender spawn-and-error-filter is written seven times: apps/mythic-masters/scripts/{beasts,flora,ground}.ts, scripts/usdz.ts, apps/codesplitter/scripts/model-review.ts, apps/splat-rooms/rooms/{build,fronts}.ts. They drift: the two splat-rooms scripts leave out --python-exit-code 1 (a traceback exits 0), only usdz.ts honours BLENDER_PATH, and each keeps a different slice of the error.

Pull one helper up (probably packages/cli, reusing findBlender from apps/meshy-studio/engine/blender.ts): -b --factory-startup --python-exit-code 1, stdout and stderr drained together, an optional -t, and the Traceback lines on failure. Delete the copies. The beast GLBs must stay byte for byte the same (-t 8 pin).

From apps/mythic-masters/docs/BLENDER-TOOLS.md, item 1.