Fix CSG intersection transform stability for downstream merges

[tracygardner]

Motivation

• Ensure CSG intersection outputs remain in the correct world/merge-space so subsequent merge/boolean operations don't lose placement or orientation.
• Preserve source orientation when applying properties to CSG result meshes so downstream consumers get the intended rotation.

Description

• Create CSG result with centerMesh: false and rebuildNormals: true when calling baseCSG.toMesh(...) so the intersected mesh is generated in world-space.
• Remove the manual recentering step (intersectedMesh.position = combinedCentre) and instead refresh the transform with intersectedMesh.computeWorldMatrix(true) to keep world placement stable.
• Stop forcing resultMesh.rotationQuaternion = flock.BABYLON.Quaternion.Identity() in applyResultMeshProperties so copied rotation/quaternion data from the reference mesh is preserved.

Testing

• Ran npm run test:api -- --grep "mergeMeshes geometry preparation|intersectMeshes" which failed in this CI environment because Playwright browser binaries are not installed (Playwright requested npx playwright install).
• Ran npm run lint which failed due to pre-existing lint issues in flock.js unrelated to this change.
• Ran npx eslint api/csg.js during development to validate the modified file; linting revealed file-level issues in the repository but the CSG-related logic changes are applied as intended.

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Codex Task