[Feature] Multi-Asset Collateral Vaults for Borrowing

[AlAfiz]

Description: Build a standalone Vault contract allowing users to lock XLM or stablecoins (USDC) as collateral to mint a synthetic stablecoin (e.g., tfUSD).
Context / Motivation: This transforms TradeFlow from a simple DEX into a comprehensive DeFi ecosystem by introducing debt markets.
Acceptance Criteria: - [ ] Contract must accept multiple Stellar assets as collateral.

• Implement borrowing logic restricted by a global COLLATERALIZATION_RATIO (e.g., 150%).
• Include a liquidate function allowing third parties to repay debt and seize collateral at a discount if a vault falls below the maintenance margin.
• Read prices securely (mock an oracle interface for now, preparing for the TWAP integration).
  Technical Pointers: State management is crucial here. Use Map or separate storage entries for individual user debt and collateral balances. Ensure arithmetic does not suffer from precision loss (use Soroban's fixed-point math conventions).

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!

[gloskull]

Hi, I would love to work on this Issue.
I have 4 years of experience delivering solutions for projects like this, covering backend, frontend, full-stack and smart contract development. After carefully reviewing your requirements, I have a clear understanding of the task and am confident in my ability to deliver a clean, efficient, and thoroughly tested solution on time. I prioritize code quality, maintainability, and industry best practices throughout the development process.
My PR will be submitted in under 10hours.