feat: add valueless mock USDC

src/MockUSDC.sol

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.35;
+
+import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
+import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
+
+/// @notice Educational mock token with no monetary value. Never use as real USDC.
+contract MockUSDC is ERC20, Ownable {
+    constructor(address initialOwner) ERC20("Mock USD Coin", "mUSDC") Ownable(initialOwner) {}
+
+    function decimals() public pure override returns (uint8) {
+        return 6;
+    }
+
+    function mint(address to, uint256 amount) external onlyOwner {
+        _mint(to, amount);
+    }
+}