M148 PR1: V2 import mapper

[Coasterpete]

Summary

• Add backend-only TrackLayoutPackageV2 import mapping into the authoring pipeline.
• Map supported V2 straight, constant-curvature, curvature-transition, spatial, banking, and constant heartline offset fields.
• Stabilize BankingProfile browser artifact path generation so deterministic tests do not depend on process-wide current directory.

Verification

• dotnet test QuantumCoasterWorks.sln --nologo
• Passed: 1698/1698