tooling: add redirect destination auditor

[huklaa]

PR Description

What changed? Why?

Adds a focused redirect destination auditor for "docs/docs.json".

The tool:

• validates internal redirect destinations against the current MDX route tree,
• follows redirect chains,
• detects redirect cycles,
• groups repeated broken destinations so large redirect migrations can be audited efficiently.

This helps address the broken redirect debt tracked in #1783 without guessing replacement targets or making unrelated redirect changes.

Notes to reviewers

This PR intentionally adds tooling only. It does not rewrite existing redirect destinations.

The default mode is report-only so the current known redirect debt does not break normal workflows. A "--strict" mode is included for targeted validation or future CI use once the redirect tree is clean.

How has it been tested?

• Added focused Node.js tests for:
  • direct valid destinations,
  • redirect chains,
  • missing terminal destinations,
  • redirect cycles,
  • external destinations,
  • path normalization.
• Verified the auditor against the current docs route tree.

[cb-heimdall]

🟡 Heimdall Review Status

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