[Spike] ISSUE-0019: deploy to Monad testnet + agent-browser E2E #24

Goal

Deploy the full MonadMon contract suite to Monad testnet (chain id 10143) and re-run the agent-browser E2E against the live deployment.

Blocked on

A funded Monad testnet wallet. The user needs to:

1. Add Monad testnet to MetaMask/Rabby: RPC https://testnet-rpc.monad.xyz, chain id 10143, symbol MON.
2. Visit the Monad faucet (https://faucet.monad.xyz), paste the wallet address, request testnet MON.
3. Export the deployer private key into .env (DEPLOYER_PRIVATE_KEY=0x...).

Steps after wallet is ready

1. cd contracts && forge install OpenZeppelin/openzeppelin-contracts@v5.1.0 --no-git (one-time).
2. DEPLOYER_PRIVATE_KEY=0x... forge script script/Deploy.s.sol --rpc-url https://testnet-rpc.monad.xyz --broadcast.
3. Save the 5 deployed addresses into frontend/.env.local (overwrite the zero addresses).
4. cd frontend && pnpm dev (auto-switches wagmi to Monad testnet because RPC URL has no 127.0.0.1).
5. agent-browser walkthrough per DEMO.md.
6. Capture screenshots + on-chain evidence into docs/evidence/0019/.
7. Open PR [Spike] ISSUE-0019: deploy to Monad testnet + agent-browser E2E #24.

Acceptance Criteria

• All 5 contracts deployed and verified on https://testnet.monadscan.com.
• All 7 MVP pages render against the live testnet addresses.
• Full happy path (mint → hatch → train → challenge → accept) verified on-chain with explorer links in the evidence.
• No mock data anywhere — leaderboard, profile, arena all read live chain state.