v0.139.0: Custom commands and skills in the slash menu and MCP fixes

New features

- Custom commands and skills in the slash menu - Your custom commands and skills now appear directly in the slash menu

Bug fixes

- MCP schema compatibility - Improved handling of MCP servers with incompatible tool schemas
- Clearing MCP server fields - You can now clear fields when editing an MCP server
- Local session labels - Local sessions are now labeled "Local" instead of "Ephemeral" (app)