Harden content audit toward invented-metric and ungrounded-citation blocks

[tph-kds]

Source: AUDIT_AND_REDESIGN_REPORT.md anti-AI-slop gates reject "decorative charts, fake metrics, or invented citations"; docs/PRODUCT_DIRECTION.md rejects "Invented metrics, references, customer logos, or product UI".

Current state: scripts/audit_deck_content.py covers duplicate titles, generic titles, repeated claims, empty content, incomplete metrics, captions, and density. It does not yet flag claims with no schema-level source reference.

Gap: generated decks can still state unverifiable numbers or cite nothing.

Acceptance:

• Audit flags metric claims lacking a backing source reference in the DeckProject schema.
• Audit flags citations whose target fails a URL reachability check when run offline-safe.
• Document the detector in docs/EXTENDING.md.