Clauses grid: show the region (not the full image) + restore 'show without thumbnail'

[lanterno]

Clauses. @pastokes:

• "Grid view thumbnail images are not working (they show the full image, not the region), but I assume this is because the text regions are not imported yet." — thumbnail should be cropped to the clause's text region (likely blocked on text-region import data).
• "There was an option to show the clause without the thumbnail image, but this no longer seems available." — restore the text-only (no thumbnail) view option.

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From UI feedback · project-discussions#8, reported by @pastokes (2026-06-29).