Implement Member Login Endpoint

Create a POST /api/v1/auth/login endpoint for members to log in.
Requirements:

Request body:

{
"email": "string",
"password": "string"
}

Validate credentials and return:

{
"token": "jwt",
"member": {
"id": 1,
"full_name": "string",
"email": "string"
}
}

Handle invalid credentials with 401 Unauthorized

Add login rate-limiting (optional)