[BOUNTY] Create Comprehensive Threat Model Document

[sayanget]

Overview

This PR provides a comprehensive threat model for the PrivacyLayer Soroban contract, fulfilling the requirements of the [Create Comprehensive Threat Model Document] bounty.

Document Summary

The document identifies:

• System Assets: User funds, nullifiers, Merkle state, and VK.
• Threat Actors: Malicious depositors/withdrawers, relayers, and compromised admins.
• Attack Vectors: Double-spend, Merkle root history exhaustion, contract DoS via panic, and VK hijacking.
• Mitigation Strategies: Detail on current defenses and future security recommendations (Multi-Sig, Address Validation).

Context

This document is based on a deep technical analysis of the PrivacyLayer codebase, including identified risks in address decoding and admin management.

[sayanget]

Claim Information

• Bounty Task: [BOUNTY] Create Comprehensive Threat Model Document
• Estimated ROI: 00+ USDC
• Payment Address (RTC): RTC89b248bde16082e0b7b9cb1b0ab29aa361a962c0