Missing reference: Hu & Rong (2025) Inter-Agent Trust Models

The references list in `architecture/07-references.md` is comprehensive on protocol specifications (MCP, A2A, AP2, ERC-8004), W3C credential standards, and IETF RFCs. One academic paper that informs the trust framework appears not to be cited.

## Suggested addition

Hu and Rong's paper directly compares trust models across A2A, AP2, ERC-8004 and other agentic protocols, and discusses several of the design choices that TSAI makes (tier model, accreditation, reputation, insurance). It is not currently in the references list.

```
**[HU-RONG-2025]**
Botao 'Amber' Hu, Helena Rong
Inter-Agent Trust Models: A Comparative Study of Brief, Claim, Proof, Stake, Reputation and Constraint in Agentic Web Protocol Design — A2A, AP2, ERC-8004, and Beyond
arXiv:2511.03434 (cs.HC), November 2025
https://arxiv.org/abs/2511.03434
```

A new subsection under Section 6.2 (Informative References), for example "6.2.5 Academic Foundations", would fit, or the entry can be added to an existing subsection.

## Confirmed already present

- MCP: https://github.com/modelcontextprotocol/modelcontextprotocol
- A2A: https://github.com/a2aproject/A2A
- AP2: https://github.com/agentpayments/ap2
- ERC-8004: https://eips.ethereum.org/EIPS/eip-8004

Open architecture/07-references.md and inspect Section 6.2, Informative References, alongside the existing protocol and standards entries. Add the supplied Hu and Rong citation in a suitable subsection, then verify the reference list includes the title, arXiv identifier, date, and URL.

Written by the indexing model from the issue text.