fix: silently hide MCP UI on errors (#10660)

fix: silently hide MCP UI on errors instead of showing broken content

When an MCP UI app can't handle a tool's data (e.g. server tags
non-UI tools with ui/resourceUri), hide the UI rather than showing
confusing error messages. Changes:
- Return null on error instead of rendering red error box
- Wrap sendToolInput/sendToolResult in try/catch
- Hide UI when MCP app reports error/critical via bridge logging