v0.87.0: Spec approval handoff, shimmer animations for tool headers, and Missions reliability improvements

New features

- Spec approval handoff - Spec approvals can now be handed off to a new session, letting you continue work separately after approving a spec

Improvements

- Shimmer animation for tool headers - Tool call headers now display a shimmer animation for improved visual feedback

Bug fixes

- Session storage reliability - Fixed duplicate save errors and added automatic recovery from permission issues in session storage
- Sidebar navigation - Fixed missing back arrow in sidebar menu titles (Factory App)
- Missions worker startup - Improved Missions worker startup reliability with extended timeout
- Missions connection stability - Increased socket connection timeout for more reliable Missions connections
- Droid Computer session creation - Fixed errors when creating sessions while the Droid Computer is temporarily unavailable (Factory App)