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>

docker/.env.example

@@ -24,3 +24,9 @@ PUBLIC_HOST=play.yourdomain.com
 # Cloudflare API Token (create at https://dash.cloudflare.com/profile/api-tokens)
 # Permissions needed: Zone > DNS > Edit
 CF_API_TOKEN=your_cloudflare_api_token
+
+# AfterCoin Blockchain (private Ethereum chain for casino tokens)
+# Generate with: node -e "const {ethers}=require('ethers');const w=ethers.Wallet.createRandom();console.log(w.address,w.privateKey)"
+AFC_ADMIN_ADDRESS=0xYOUR_ADMIN_ADDRESS
+AFC_ADMIN_PRIVATE_KEY=your_private_key_without_0x_prefix
+AFC_BRIDGE_SECRET=change_me_in_production