Add configurable Transform Snap increments and publish Beta 13

[WebCrew]

Summary

• add a compact Transform Snap settings dialog beside the existing toggle
• configure validated Move, Rotate and Scale increments
• persist settings locally without dirtying scene data
• keep Inspector values unrestricted and preserve 2.5D axis constraints
• add Reset Defaults, automated UI contracts, roadmap status and Beta 13 acceptance coverage

Verification

• node scripts/check.cjs
• git diff --check
• exact GitHub comparison against the Beta 12 main commit

Parlyn CI, CodeQL and the Windows Installer workflow must all pass before merge.