feat: Soroban USDC vault contract

[collinsezedike]

Summary

• Implements the MeridianVault Soroban smart contract in packages/contracts/vault/src/lib.rs
• Users deposit USDC and receive proportional mUSDC shares; shares appreciate as yield accrues
• deposit accepts a Protocol parameter (Blend | DeFindex) resolved off-chain at call time, so the user signs the routing decision before submission
• withdraw burns mUSDC shares and returns proportional USDC back to the caller
• View functions: get_position, get_active_protocol, get_total_assets, get_total_shares
• Test snapshots committed and marked linguist-generated in .gitattributes to suppress noise in GitHub diffs

Test plan

• cargo test passes all 4 tests: deposit_mints_shares, withdraw_returns_usdc, share_price_reflects_yield, withdraw_more_than_balance_panics
• share_price_reflects_yield confirms a second depositor receives fewer shares after yield accrual
• withdraw_more_than_balance_panics confirms the contract panics with "insufficient shares"
• Snapshot files in test_snapshots/ are collapsed in the GitHub diff (linguist-generated)

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Project	Deployment	Actions	Updated (UTC)
meridian	Ready	Preview, Comment	May 24, 2026 5:13pm