Add Confidential Note Fungible Token test suites

🧐 Motivation

The only tests in #679 cover the crypto/NoteDelivery primitive. Nothing exercises the token modules, so every safety and privacy property in the design doc is currently unverified.

📝 Details

• Encode the confidential-note-token.md §12 invariants as Vitest specs: value conservation, single-spend via nullifiers, membership soundness, issuer/authority gating, auditor completeness (no output exists that the audit key cannot open), freeze/seize mutual exclusion, allowlist revocation.
• Simulators and witness harnesses for every module already landed in #679 — the suites are the missing half.
• Include negative cases: wrong witness, replayed nullifier, stale Merkle root, non-allowlisted spender, unaudited output.

Planned, not in #679 (confidential-note-token.md §0).