Preserve related entries in Salesforce Help docs

[clavery]

Summary

• Preserve direct child topic relationships from Salesforce Help DITA maps.
• Add a Related Content section to generated Help Markdown and expose exact child IDs through relatedEntries metadata.
• Keep chunked descendant topics embedded in their parent page rather than treating them as related standalone pages.
• Surface related entry IDs in CLI/MCP read output and offline fallback content.
• Regenerate the Help corpus: 192 landing articles now expose 960 validated relationships.

This retains the upstream Help sourceUrl read fix from #576.

[github-actions]

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