fix(jsonview): preserve literal object keys in pretty output and explorer

[Ultron09]

Summary

Preserve literal object keys across pretty formatting and the interactive JSON explorer instead of resolving member names containing dots or metacharacters as GJSON query paths.

Fixes #81.

Problem & Root Cause

The JSON renderer and explorer enumerate literal member names with @keys / gjson.Result.Get("@keys"), but subsequently fetched each value through result.Get(key.Str), data.Get(key.Str), or item.Get(key).

Because GJSON interprets string arguments to .Get() as path expressions (such as evaluating "a.b" as a traversal into nested object a -> b), keys with dots or other GJSON path syntax either:

1. Display a nested child value under a top-level key's label, or
2. Fail to find any value and display empty/null even when the literal key exists.

Fix

Materialize the object map once with result.Map() and look up values by exact literal key:

• internal/jsonview/staticdisplay.go: formatJSONObject
• internal/jsonview/explorer.go: newObjectTableView, newArrayOfObjectsTableView, TableView.loadMoreData, and formatObject

Regression Coverage

Added comprehensive regression tests in internal/jsonview/literal_keys_test.go:

• TestStaticDisplayUsesLiteralObjectKeys: confirms static pretty formatting preserves top-level dotted keys and nested paths concurrently.
• TestExploreTableUsesLiteralObjectKeys: confirms object table view and array-of-objects table view display the literal key's value.
• TestExploreFormatObjectUsesLiteralObjectKeys: confirms object previews format literal keys correctly.

Validation Commands & Results

• go test -v ./internal/jsonview/... (PASS)
• go test ./pkg/cmd -run TestFormatJSON (PASS)
• go vet ./internal/... ./pkg/... (PASS, clean)
• go mod verify (PASS, all modules verified)
• git diff --check (PASS, clean)

[sylvesterkaczmarek]

Checked the affected renderer/explorer paths. @keys still supplies object/column order, while Map() is now only used for exact literal lookup, so dotted or metacharacter keys can't be reinterpreted as GJSON paths. columnKeys is also preserved for paged rows. The static, object-table and array-of-object regressions cover the main paths. Looks consistent.