docs(reference): add third-party audit summary page

[theo372001]

Summary

Adds a curated, non-technical summary page for Wraith Protocol's contract audits, per #86.

• New reference/audits.mdx — one section per audit with firm, date, scope, findings summary (severity + description per finding), and remediation status, linking to the raw report.
• Note: the repo currently has exactly one completed audit — a Stellar Asset Contract (SAC) compatibility review conducted internally by the Wraith Protocol security team, not by a third-party firm. The page states this explicitly rather than overstating it, per the "copy reviewed for accuracy vs raw reports" acceptance criterion. Additional third-party audits are noted as planned, with a pointer to the roadmap.
• Nav entry added under "Reference" in docs.json.
• While editing that nav array I found (and fixed) a pre-existing invalid-JSON syntax error in the same "Reference" group — a duplicate/malformed pages key left over from a bad merge in 5c5c7f1/23d0a1f, which broke docs.json parsing entirely (unrelated content, e.g. contracts/evm/contracts/stellar/etc., remains reachable via the separate, untouched "Contracts" group). Had to fix it since it's the exact object this PR's nav entry needed to go into.

Type

• Documentation

Related Issue

Closes #86

Testing

• node -e "JSON.parse(...)" on docs.json: now valid (was failing before this fix).
• mint validate: the only remaining failures are pre-existing and unrelated, confirmed via git stash comparison against clean develop — a genuine MDX parse error in contracts/stellar.mdx (stray ! character) and a dangling nav reference to reference/stellar-event-schemas, a file that has never existed in the repo. My new reference/audits entry produces zero warnings.
• mint broken-links couldn't complete, blocked by the same pre-existing contracts/stellar.mdx parse error.
• Findings summary cross-checked against the raw report (contracts/stellar/audits/2026-06-sac-compatibility.md) for firm name, date, and all 7 finding IDs/severities.