Fix projected graph body validation

[Widthdom]

Summary

• Preserve parsed --body intent independently of bounded --fields projection for references, refs, callers, and callees.
• Skip body materialization when an explicit projection excludes body fields while retaining validation order and compact-location output contracts.
• Add regression coverage for graph commands and aliases across explicit/all fields, compact variants, field discovery, pagination, and primary validation errors.

Validation

• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-restore --filter FullyQualifiedName~JsonEnvelopeWrapperIssue4882Tests --framework net8.0 — 7 passed
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-restore --filter FullyQualifiedName~JsonEnvelopeWrapperIssue4882Tests --framework net9.0 — 7 passed
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-restore --filter FullyQualifiedName~JsonEnvelopeWrapper --framework net8.0 — 68 passed
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-restore --filter FullyQualifiedName~JsonEnvelopeWrapper --framework net9.0 — 67 passed, 1 skipped
• Full suite before review fixes: net8.0 — 11,640 passed, 7 skipped; net9.0 — 11,161 passed, 423 skipped
• dotnet build CodeIndex.sln -c Release --no-restore -p:UseSharedCompilation=false
• make lint
• dotnet run --project tools/CodeIndex.Changelog -- check — 28 fragments validated
• Exact issue reproduction exits successfully with the requested projection and no body fields emitted
• Root index and workspace manifest checks are healthy at the final HEAD
• Mandatory codex review --base origin/main completed in two rounds; all actionable findings were addressed and post-fix regression tests pass

Documentation and changelog

• Updated both the English and Japanese projection-semantics sections in USER_GUIDE.md.
• Added changelog.d/unreleased/5094.fixed.md with English and Japanese entries.

Follow-up candidates

• Return an empty compact envelope for zero-match callees queries #5128 tracks the pre-existing zero-match callees --compact empty-row contract discovered during review; it is intentionally outside this fix.

Fixes #5094