Add nested inspect field projections

[Widthdom]

Summary

• Add typed, one-level collection.field projections to cdidx inspect, including canonical parent/alias/order handling and queryless --fields list discovery.
• Preserve root response metadata, coupled row truncation metadata, definition-body recovery, compact output, partial-family details, and byte-budget behavior.
• Return structured catalog-backed usage errors for unknown selectors and document the contract in both English and Japanese.
• Add regression coverage for nested rows, duplicate options, body-loading boundaries, genuinely truncated contexts/signatures/partial families, catalogs, errors, and bounded output.

Validation

• dotnet build CodeIndex.sln -c Release --no-restore — 0 warnings, 0 errors
• Inspect/projection regression surface — .NET 8: 153 passed; .NET 9: 152 passed, 1 skipped
• Issue Add nested field projections to inspect JSON output #5098 focused tests — .NET 8/9: 2 passed each
• dotnet format CodeIndex.sln --verify-no-changes --no-restore
• dotnet run --project tools/CodeIndex.Changelog -- check — 32 fragments validated
• Initial full-suite run — .NET 8: 11,650 passed, 7 skipped; .NET 9: 11,171 passed, 423 skipped
• Two Codex adversarial-review rounds completed; all actionable findings were fixed and revalidated

Follow-up

• Keep post-extraction hook fixture discovery below the loadable-type cap #5135

Fixes #5098