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/genesis.json

@@ -0,0 +1,27 @@
+{
+  "config": {
+    "chainId": 8888,
+    "homesteadBlock": 0,
+    "eip150Block": 0,
+    "eip155Block": 0,
+    "eip158Block": 0,
+    "byzantiumBlock": 0,
+    "constantinopleBlock": 0,
+    "petersburgBlock": 0,
+    "istanbulBlock": 0,
+    "berlinBlock": 0,
+    "londonBlock": 0,
+    "clique": {
+      "period": 5,
+      "epoch": 0
+    }
+  },
+  "difficulty": "0x1",
+  "gasLimit": "0x1C9C380",
+  "extradata": "0x0000000000000000000000000000000000000000000000000000000000000000751c6F0Efd9B97A004969cfF9ACfA32230bdC4c40000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
+  "alloc": {
+    "0x751c6F0Efd9B97A004969cfF9ACfA32230bdC4c4": {
+      "balance": "0xffffffffffffffff"
+    }
+  }
+}