[tooling] Anvil BSC mainnet fork script for local end-to-end demo

[obchain]

Goal

Local anvil fork of BSC mainnet so the full liquidation path (scanner → profit → Aave V3 flashloan → Venus liquidate → PancakeSwap swap) can be demonstrated without real funds.

Scope

• New script: scripts/anvil_fork.sh
  • Primary RPC: https://bsc.drpc.org (free, archive, keyless)
  • Fallback: https://bsc-rpc.publicnode.com
  • Preserve chainId 56 via --chain-id 56
  • Pin fork block via FORK_BLOCK env var (default: latest)
  • Expose :8545 HTTP + WS
• New file: config/fork.toml mirroring mainnet config with RPC http://127.0.0.1:8545
• README section: fork demo steps

Acceptance

• ./scripts/anvil_fork.sh boots anvil and prints fork block
• charon --config config/fork.toml test-connection prints the forked head
• Fork survives >100 blocks of charon scanning without crash