Bugs and test-coverage gaps: catalog items do not work as expected.

[polina-c]

This should be fixed and test covered:

• Example for 'checkBox' does not work
• MultipleChoice shows check boxes, not radio buttons, even when `"maxAllowedSelections": 1 (see Add example with "maxAllowedSelections": 1 #451)
• Example for catalog item 'modal' does not work
• Add description to catalog items to improve quality of generated UI

Screen.Recording.2025-10-26.at.12.02.14.PM.mov

Screen.Recording.2025-10-26.at.12.25.48.PM.mov

        {
          "id": "root",
          "component": {
            "MultipleChoice": {
              "selections": {
                "path": "/mySelections"
              },
              "maxAllowedSelections": 1,
              "options": [
                {
                  "label": {
                    "literalString": "Radio Button 1"
                  },
                  "value": "1"
                },
                {
                  "label": {
                    "literalString": "Radio Button 2"
                  },
                  "value": "2"
                }
              ]
            }
          }
        }

[victoreronmosele]

Example for 'checkBox' does not work

I fixed this here.