fix: stop completed persistent background playback from replaying

[han4wluc]

Summary

• keep persistent background animation selections attached while the background remains unchanged
• stop inherited persistent background animations from re-emitting after their finite playback has already finished
• bump the package patch version to 1.6.1

Validation

• bunx vitest run puty.spec.js spec/RouteEngine.rollbackRenderState.test.js
• bunx vitest run spec/RouteEngine.rollbackRenderState.test.js --testNamePattern "inherited persistent background animation|persistent background playback"
• regenerated VT candidate pages with bun run vt:generate
• verified http://localhost:3004/candidate/background/playback-persistent-transition-dialogue-continuity in the browser after waiting for completion and clicking to line 2; the door crop brightness stayed unchanged (YAVG 117.992 -> 117.992), confirming the animation did not restart