Add multi-query audit output for cdidx search

[Widthdom]

Found while dogfooding the locally built cdidx on branch codex/search-audit-issues-20260619.

Duplicate check: no open issue found for multi-query search audit summary JSON array output.

Observation:
Broad audits required running many independent cdidx search queries, then grouping results by query and filtering noisy matches outside the tool.

Problem:
A native multi-query audit mode would reduce orchestration overhead and make broad CodeIndex self-audits more reproducible.

Acceptance criteria:

• Add a CLI mode or recipe option that runs multiple search queries in one command.
• Return query-grouped JSON with per-query counts, top paths, and truncation metadata.
• Support bounded output so broad audits do not require external post-processing.
• Add tests and help text for multi-query audit output.

[Widthdom]

Work started on branch fix-issue3787-3714-3731-3710-3694-3693-3670-3696.