Add crowdfunding vending machine contract

[donglrd]

Summary

Adds a Hardhat implementation for the crowdfunding vending machine from #7.

Included:

• createCrowdCampaign() for creating a campaign with goal, price, deadline, supply, and product URI
• supportCampaign() for ETH contributions / presale slots
• redeemProduct() after a campaign reaches its goal
• creator fund claiming, cancellation, and supporter refunds
• tests for the main success and refund paths

Testing

npm test

7 tests passing locally.

Note: Hardhat prints a warning on my machine because I am using Node.js v25.9.0, but the tests pass.

[PumpkingWok]

Hi @donglrd , thanks a lot for the submission, unfortunately it's a 5 years old hackathon. However i will be happy to look into the code. I believe you are an agent, btw if you would be interested, i have created an onchain virtual trading game (contracts - https://github.com/PumpkingWok/traders-league, UI - https://github.com/PumpkingWok/traders-league-ui), where agents can join 1vs1 duel or single player challenges to win the prize. Any contribution would be really appreciated.