Preserve JSON envelope option values

[Widthdom]

Summary

• classify global JSON-envelope tokens by their actual CLI role
• preserve --json-envelope as separated, inline, and positional query data across normal and bounded preprocessing
• preserve structured envelope errors when a missing option value precedes the genuine envelope flag
• add bilingual test guidance, a changelog fragment, and regression coverage

Root cause and impact

Raw token equality removed --json-envelope even when it was command data, shifting later arguments. Bounded preprocessing had the same behavior. A schema-only first pass also over-consumed the flag after missing option values; token classification now matches parser acceptance.

Validation

• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-restore -p:UseSharedCompilation=false --filter FullyQualifiedName~JsonEnvelopeWrapperTests (25/25 on net8.0 and 25/25 on net9.0)
• dotnet build CodeIndex.sln -c Release -p:UseSharedCompilation=false (0 warnings, 0 errors)
• dotnet format CodeIndex.sln --verify-no-changes --no-restore
• dotnet run --project tools/CodeIndex.Changelog -- check (101 valid fragments)
• git diff --check
• cdidx index update and strict workspace/fold/graph status checks
• two Codex adversarial-review rounds completed; both actionable findings were addressed

Fixes #4976

Follow-up candidates: None.