Make batch a structured read-only query transport

[Widthdom]

Summary

• Define the batch allowlist from the command schema and include side-effect-free goto and audit queries.
• Return typed result/results payloads for JSON and NDJSON while preserving raw stdout for text and failures.
• Preserve per-command exit/error metadata and bound input lines plus the complete serialized output stream.
• Document and test the transport contract in both English and Japanese, including command-specific and case-insensitive output formats.

Validation

• dotnet build CodeIndex.sln -c Release --no-restore
• dotnet test CodeIndex.sln -c Release --no-build -m:1 (net8.0: 9512 passed, 6 skipped; net9.0: 9076 passed, 384 skipped)
• Focused batch tests: 20 passed on net8.0 and 20 passed on net9.0
• dotnet format CodeIndex.sln --verify-no-changes --no-restore
• Changelog fragment validation
• git diff --check
• Codex adversarial review: two rounds completed; all actionable findings addressed

Fixes #4582