* feat(studio): preview new tracks at drop boundaries
* fix(studio): preserve group ownership across overlapping moves
* refactor(studio): share timeline drop decisions and fixtures
* fix(studio): open an empty audio zone below visual tracks
* fix(studio): cancel thumbnails when project pages leave
* refactor(studio): share thumbnail regression setup
* test(studio): gate thumbnail socket release in browser CI
* chore(studio): keep optimistic revision comments within ratchet
* fix(studio): pin regression proxy requests to its backend
* test(studio): bound the proxy origin probe
* test(studio): probe proxy origin through the ready document