On-chain settlement on Arbitrum Sepolia

[ozpool]

Problem

Today every contract (CollateralVault, PositionRegistry, MarketRegistry, OracleAdapter, MockUSDC, MockOracle) deploys to local anvil only. No public testnet presence.

For the next investor cycle and the v1.1 milestone we want a wallet to bridge real testUSDC, sign EIP-712 orders, see positions settle on-chain, and have a block explorer link to point at.

Proposal

1. Add script/DeploySepolia.s.sol mirroring Deploy.s.sol but pointing at Pyth's real OracleAdapter (no MockOracle — the relayer already speaks Pyth Hermes and produces the VAA bytes via HermesSource).
2. Faucet path: deploy a testUSDC (or use an existing Sepolia USDC) with a 1k mint per address per 24h.
3. CI workflow that runs forge build + forge verify against Sepolia on tag pushes.
4. Edge --rpc-url flag — point it at the Sepolia RPC and the deployed contract addresses instead of anvil.
5. .env.example template: SEPOLIA_RPC_URL, DEPLOY_PRIVATE_KEY, ARBISCAN_API_KEY.

Acceptance

• All four contracts verified on arbiscan-sepolia.
• Demo wallet can deposit testUSDC, place an order, see the position open on-chain (positionRegistry shows the entry), close and confirm USDC returned.
• One liquidation runs end-to-end on Sepolia (positions opened with thin margin, oracle drops, liquidator process forces close, bonus paid).

Depends on

#151 (liquidator) for the full E2E run.