Add a traversal-safety audit recipe for directory enumeration paths

[Widthdom]

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

Duplicate check: no open issue found for filesystem traversal audit recipe Directory.EnumerateFiles cancellation budget exception taxonomy.

Evidence:

• Directory.EnumerateFiles appears in solution/project discovery, file indexing, checkpoint inspection, plugin discovery, and hook discovery.
• Some paths include budgets and cancellation; others mainly rely on exception handling.

Problem:
Traversal behavior is a recurring source of performance, permission, and cancellation risk. A focused recipe would make it easier to audit new enumeration paths consistently.

Acceptance criteria:

• Add a built-in audit recipe for directory enumeration and traversal APIs.
• Include notes or filters for cancellation checks, traversal budgets, long-path handling, and exception taxonomy.
• Add tests for recipe listing and at least one expected match.

[Widthdom]

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