Fix checkbox parameter display issues

[cdr-robot]

Summary

• Always show parameter label at the top for all parameter types consistently
• Add support for custom checkbox label text via styling.label property
• Default checkbox label to \Enable\ for better UX when no custom label is provided

Fixes #25

Test plan

1. Create a template with checkbox parameters using both approaches:
   • Standard checkbox parameter
   • Checkbox parameter with styling.label property

This PR addresses the issue where checkbox parameters show the display name twice in the UI, by:

1. Always showing the parameter name/display name at the top (consistent with other parameters)
2. Using a custom label or default \Enable\ text next to the checkbox
3. Supporting the styling.label property as proposed in the original issue

Workspace URL: https://demo.coder.com/ben/issue-25