Access control — Ownable pattern

solidity
import "@openzeppelin/contracts/access/Ownable.sol";

contract Vault is Ownable {
    constructor() Ownable(msg.sender) {}

    function withdrawAll(address payable to) public onlyOwner {
        to.transfer(address(this).balance);
    }
}

• owner() — public view of the current owner
• onlyOwner modifier — reverts if msg.sender != owner
• transferOwnership(address) — owner can hand over control
• renounceOwnership() — owner can burn ownership (contract becomes uncontrollable)

• Admin-only setters (change fee, pause, upgrade)
• Emergency withdrawals
• Minting privileged tokens

Ownable gives ONE role. Real systems have MULTIPLE roles (minter, pauser, treasurer). Use AccessControl for role-based permissions — we'll cover that next.

Write a Treasury contract that: 1. Inherits Ownable 2. Holds ETH 3. Has a sendTo function only the owner can call, which sends a given amount to an address