Prepare Pet mode video handoff

[codeugar]

What changed

• give Pet / Kid mode a dedicated five-second preparation countdown
• hide CleanMyScreen as soon as that countdown begins so the previous app is ready for opening or full-screening a video
• add a compact in-app explanation of the handoff behavior
• keep Cleaning and Selective mode countdowns at three seconds
• harden app bundle verification in File Provider-managed workspaces
• bump the app to 0.1.3

User impact

After pressing Start in Pet / Kid mode, CleanMyScreen immediately gets out of the way and the user has five seconds to prepare their video before keyboard and trackpad input are locked.

Validation

• ./Scripts/run-tests.sh — 11 tests passed
• ./Scripts/build-app.sh
• visual QA of the Pet / Kid first-screen layout
• arm64 and x86_64 DMGs mounted and verified for version, architecture, code signature, and SHA-256 checksum