Row JSON expand viewer causes memory issues on large values #33

Expanding a row whose JSON is very large (e.g. a Buffer serialized as a data byte array of thousands of numbers, or large jsonb) causes high memory use / sluggishness.

Cause
The raw-view preview truncated long strings but kept every array item and object key, so the stringified text ballooned and then got syntax-highlighted (a span per token).

Requested / Expected
For large values, do not run syntax highlighting, and bound the preview breadth. Full value should still be available via Copy JSON.

Addressed by #23.