audit: define genre handling when a page has no declaration

[echo719]

What happens

audit.md currently defines genre-aware grading only when the audited page already has a Hallmark stamp. Third-party pages usually have neither a Hallmark stamp nor design.md, so genre-scoped gates can change severity without the audit explaining which genre it applied.

I hit that boundary while auditing a real, unstamped homepage. The result was 0 critical · 1 major · 3 minor, but the only major depended on treating the page as editorial. The same page also carried both AI-tool and developer-tool signals, which point to two non-default genres in the Design flow.

The change

Adds one rule to the audit verb:

• infer an undeclared genre from visible product and design signals using the existing Design-flow table;
• state the inference and evidence before findings;
• when two non-default genres have comparable evidence, declare the ambiguity and apply only universal gates instead of escalating a genre-scoped rule.

This keeps the audit deterministic without forcing a third-party page to contain Hallmark metadata.

Verification

• Current main: aeb42fb
• Docs/skill-instruction-only change; no runtime surface
• Existing stamp and design.md behavior is unchanged
• git diff --check passes
• No same-topic PR or issue found

The unstamped audit that exposed the gap is published with its other findings here: https://skillstested.com/compare/hallmark-vs-kill-ai-slop-vs-visual-skills/

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