v0.28.0: Session management, slash command navigation, thinking improvements, and Figma MCP support

New features

- Show all sessions - View and manage all your sessions across directories
- Windowed slash command navigation - Improved navigation in the slash command menu with windowed scrolling
- Improved thinking display - Refactored thinking block rendering for better clarity
- Figma MCP server - Added support for Figma MCP server integration

Bug fixes

- Fixed detection of Cerebras-style context length exceeded errors
- Fixed duplicate spec modes and double empty line above input
- Added promo price label for Opus model
- Fixed /install-github-app command issues