Smart contract for saving rules

**Goal:** On-chain proof of savings (immutable record of member deposits).

**Explanation:**
This contract handles how much each member contributes, time, and rules like minimum deposit.
Ensures fairness and prevents tampering.

**Key Functions:**

- `deposit()`

- `getMemberSavings(address member)`

- `setMinimumDeposit(uint amount)`

**Deliverables:**

- `contracts/SavingsContract.sol`

- Unit tests: deposit + query savings balance

Start with the requirements in the issue and inspect the existing contracts/ directory before creating contracts/SavingsContract.sol. Define how deposits, member savings queries, minimum deposits, timestamps, and immutable records should behave, then add unit tests covering deposit and savings-balance queries. Done means the contract implements the listed functions and the tests pass.

Written by the indexing model from the issue text.