fix(jsonview): preserve literal keys throughout the interactive explorer

[sylvesterkaczmarek]

Summary

Make every interactive JSON-explorer object lookup use literal JSON member names instead of interpreting those names as GJSON path expressions.

This complements #86, which addresses the same class of bug in the static pretty renderer. The interactive explorer has its own independent lookup paths and remains affected without this change.

Related to #81.

Problem

The explorer enumerates real object member names with @keys, but several rendering paths then feed those names back into gjson.Result.Get. Get parses its argument as a GJSON path, so a literal key such as a.b can resolve the nested path a -> b instead of the top-level member named exactly a.b.

For example:

{
  "a.b": "literal-value",
  "a": {"b": "nested-value"}
}

can show nested-value under the a.b key even though the underlying JSON stores literal-value there.

The bug exists in four interactive paths:

1. ordinary object tables;
2. array-of-object tables;
3. compact object previews;
4. rows appended later by the streaming/lazy-load iterator.

Fixing only one of these leaves the same incorrect value substitution elsewhere in the explorer.

Fix

Once keys have been enumerated, materialize each object's literal map with Result.Map() and index it directly by the key string. No GJSON path parsing is used for an already-known object member name.

The change covers all four interactive paths above while leaving genuine navigation-path construction and user transformations unchanged.

Regression coverage

Added focused tests proving literal dotted keys remain distinct from nested paths in:

• object-table rendering;
• array-of-object column rendering;
• compact object previews;
• lazy-loaded streamed rows.

The fixtures deliberately contain both "a.b" and nested {"a":{"b":...}} values so a path-based lookup deterministically returns the wrong value before the fix.

Validation

The branch is based directly on current upstream main (a7719136b8ed401b0c51a05553a5e4f720150307) and contains one DCO-signed commit. The production change is 9 additions / 4 deletions in handwritten internal/jsonview/explorer.go, plus focused regression coverage. Full repository test execution is left to CI.

Risk

Low. The explorer already has the literal member names. This change only stops reinterpreting those names as query expressions. Simple keys retain the same values, while keys containing GJSON path syntax now correctly refer to their own object members.