Grid styling

In Enketo, `grid` can be applied at the form level to modify the layout of an entire form: https://blog.enketo.org/gorgeous-grid/ It was designed primarily to make printable forms and forms for computer data entry and works really well for those cases.

Users choose it because the find the layout and styling visually appealing.

It also makes repeats more compact and somewhat easier to use:

Sometimes it would be helpful to be able to insert a grid into a form that has a top-to-bottom layout. We have discussed also having a grid appearance to satisfy that need.

The main challenge with Enketo's current grid is that because it's a "theme", a lot of customizations that would make sense to apply to both (e.g. colors) must be specified separately.

No file, test, or entry point is named. Start by reviewing Enketo’s existing form-level grid theme and the linked grid examples, then clarify whether the goal is an inline grid appearance, shared styling customization, or both; done should include an agreed scope and documented behavior for grid layouts and repeats.

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