Tighten prompt_template_source.notes: explicit 5-tier classification per 2026-06-01 priority rules

Refine prompt_template_source: cite verifiable official sources per 2026-05-30 deep audit

Populate prompt_template_source for all subsets per 2026-05-30 audit

2026-05-28 prompt-template audit: align to authoritative source

fix metadata.json source.url key test->train to match actual split

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