feat: add AfterCoin (AFC) private blockchain for Minecraft casino

Private Ethereum chain (Clique PoA, chain ID 8888) with ERC-20 token
(0 decimals, 1 AFC = 1 diamond) bridging casino balances on-chain so
players can view tokens in MetaMask.

- Geth v1.13.15 node with 5s block time, zero gas cost
- AfterCoin ERC-20 contract with owner-gated mint/burn/bridgeTransfer
- Bridge API (Express + ethers.js + SQLite) with register, deposit,
  withdraw, balance, and wallet endpoints
- Nonce queue for serial transaction safety
- Auto-deploys contract on first boot
- Updated mainframe Lua with diff-based on-chain sync (pcall fallback)
- Updated card generator Lua with wallet info display

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

blockchain/Dockerfile

@@ -0,0 +1,12 @@
+FROM ethereum/client-go:v1.13.15
+
+COPY genesis.json /app/genesis.json
+COPY init-geth.sh /app/init-geth.sh
+
+RUN chmod +x /app/init-geth.sh
+
+EXPOSE 8545 8546
+
+WORKDIR /app
+
+ENTRYPOINT ["/app/init-geth.sh"]