add demo for week7

contributions/demo/week7/yuz2/README.md

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+# Assignment Proposal
+
+## Title
+Fair Play in Open Cards: Implementing Commit-Reveal Voting
+
+## Names and KTH ID
+- Yu Zhang (yuz2@kth.se)
+
+## Deadline
+- Week 7
+
+## Category
+- Demo
+
+## Description
+Public blockchains face a "transparency paradox": transparency is good for trust, but bad for game theory. In voting or auctions, if I see your transaction in the mempool, I can copy it (copy-cat voting) or outbid it immediately (front-running).
+
+This demo solves the "Transparency Paradox" (front-running) in blockchain voting using the Commit-Reveal Scheme. I will deploy a voting contract in Remix to demonstrate:
+
+- Commit Phase: Submitting a hash of the vote + salt (hiding the choice).
+
+- Reveal Phase: Revealing the original data to verify and count the vote.
+
+- Live Cheating: Attempting to change the vote during the reveal phase to show how the contract mathematically prevents fraud.
+
+**Relevance**  
+This pattern is fundamental for Programmable Society applications that require fairness, such as Sealed-Bid Auctions (like ENS names), Gambling, and privacy-preserving Voting. It demonstrates how to achieve temporal privacy on a completely public ledger without needing complex ZK-proofs.