feat: add code folding

[philippfromme]

Proposed Changes

Adds cold folding. I didn't adjust the styling, it's the same styling as in the Desktop Modeler XML editor.

Closes #71
Related to camunda/camunda-modeler#5598

Checklist

Ensure you provide everything we need to review your contribution:

• Your contribution meets the definition of done
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[Copilot]

Pull request overview

This PR adds code folding functionality to the Output Editor to improve readability of large JSON outputs. The implementation uses CodeMirror's built-in folding features, including the fold gutter UI and keyboard shortcuts.

Changes:

• Added code folding support to the Output Editor using CodeMirror's foldGutter and foldKeymap extensions
• Imported necessary folding utilities from @codemirror/language and keymap from @codemirror/view

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[barmac]

We probably don't want to show the gutter for a deployment failure:

[barmac]

It looks OK on the happy path:

[barmac]

Let's fix #70 (comment)

[jarekdanielak]

@philippfromme is this ready for a final review?