fix(docs): repair structured data from brain #32

[MSKazemi]

Summary

Fix the structured-data defects tracked in MSKazemi/brain#32.

• emit breadcrumb items only for navigable ancestors
• give every emitted breadcrumb ListItem an absolute item URL with contiguous positions
• omit the homepage's ineligible single-item breadcrumb
• type Dataset.creator explicitly as Person
• update structured discovery surfaces from 88 to the current 90 tasks
• extend scripts/seo_check.py to audit JSON-LD across every built docs page so this class is regression-gated

The change intentionally does not modify benchmark/scoring behavior.

Substantial AI assistance was used to prepare and verify this patch.