v0.28.1: Certificate caching, image upload limits, and settings rendering fixes

- Certificate caching - Certificates are now cached on startup for faster loading
- Image upload limits - Conversation images are now limited to prevent 413 errors when uploading large images
- MCP registry helper - Added note for STDIO servers in MCP registry explaining installation requirements

Bug fixes

- Fixed invalid signature in thinking block after assistant message interrupt
- Fixed settings menu not showing all options when loading asynchronously