Auditor onboarding + PoC template

[truthixify]

Tier: S (1-2 days) | Type: docs

Context. reference/security-disclosure.mdx and reference/threat-model.mdx landed in Wave 7 but there is no on-ramp for a researcher who wants to actually file a finding: no repro-repo template, no severity matrix, no reward posture spelled out. Auditors expect a one-page "start here" that mirrors what large protocols publish.

Scope.

• New reference/auditor-guide.mdx.
• Severity matrix (Critical/High/Medium/Low) with concrete Wraith-shaped examples.
• Reward posture (or explicit "reputation-only" if that is the current state).
• PoC repo template link + expected structure (README, repro script, expected output).
• SLA table (ack, triage, fix, disclosure).
• Cross-link with security-disclosure.mdx and threat-model.mdx.

Acceptance.

• Severity examples reviewed by contracts maintainer
• Template repo link resolves
• Renders in mint dev
• Passes Compile docs snippets CI
• Linked from both security-disclosure.mdx and per-repo SECURITY.md

Files. reference/auditor-guide.mdx (new), reference/security-disclosure.mdx.