[contracts] Foundry workspace + CharonLiquidator.sol skeleton

[obchain]

Context

The on-chain executor. Solidity lives in a dedicated Foundry workspace (contracts/) separate from the Cargo workspace. CharonLiquidator.sol is the single-contract entry point that flash-borrows, liquidates, swaps collateral back, repays, and forwards profit.

Scope

• Create contracts/ directory with foundry.toml + lib/ for OpenZeppelin, Solmate, Aave-v3, Venus interfaces
• contracts/src/CharonLiquidator.sol skeleton with:
  • onlyOwner gate
  • executeLiquidation(params, flashSource) entry point
  • Empty receiveFlashLoan / executeOperation callbacks
• contracts/src/interfaces/ with Aave V3 Pool, Venus Comptroller, Venus VToken, Uniswap/PancakeSwap V3 Router interfaces
• foundry.toml configured for Solidity 0.8.24+, remappings, optimizer on (200 runs)

Acceptance criteria

• forge build in contracts/ succeeds
• Directory layout follows Foundry conventions (src/, test/, script/, lib/)
• CharonLiquidator inherits IFlashLoanSimpleReceiver from Aave V3
• Contract compiles but reverts in callbacks (until issue for full wiring lands)
• Remappings resolved (@openzeppelin/, @aave-v3/, etc.)

References

• PRD section 5b (Solidity Liquidator Contract)

[obchain]

Superseded — Foundry skeleton shipped in feat/11-foundry-skeleton.