fix(jsonview): avoid width underflow in static string rendering

[sylvesterkaczmarek]

Summary

Avoid converting a negative remaining display width into an enormous unsigned truncation limit when rendering static JSON strings in narrow terminals.

Problem

formatResult currently truncates long strings with:

truncate.String(str, uint(width-1))

Object and array rendering can pass a non-positive width after subtracting the rendered key or numbering width. Converting width-1 to uint then wraps the negative value to a very large number, so the string is effectively not truncated and can spill far beyond the available terminal width.

Fix

Centralize string-width handling in a small helper that:

• returns no string content when no width is available;
• renders a single ellipsis when exactly one column is available;
• preserves strings that already fit;
• only converts a verified positive truncation width to uint.

Normal-width output is unchanged.

Regression coverage

Added focused tests covering:

• a non-positive string width, which previously retained the full string because of unsigned wraparound;
• the one-column case, which now deterministically renders a single ellipsis.

Validation

The branch is based directly on current upstream main (ee92673a416c0851a5fe8907a2453db7bd450633) and contains one signed commit touching only the static JSON renderer and its focused regression test. Full Go test execution is left to repository CI.

Risk

Low. The behavior change is limited to string values whose available display width is zero or too small to contain the original value.