Write basic smart contract for Chama

**Goal: **Create a base Solidity smart contract that all others will extend.

Explanation: Define common structs and events (e.g., Member, Loan, Group). This becomes your “ChamaaCore.sol”.

Contents:

• Structs: Member, LoanRequest, TransactionRecord.

• Events: LoanRequested, LoanApproved, ContributionMade.

• Modifiers: onlyMember, onlyAdmin.

Deliverables:

• contracts/ChamaaCore.sol

• Compiles without warnings in Hardhat/Remix.