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>

services/afc-bridge/src/db.js

@@ -0,0 +1,64 @@
+const Database = require("better-sqlite3");
+const config = require("./config");
+
+const db = new Database(config.DB_PATH);
+
+// Enable WAL mode for better concurrent read performance
+db.pragma("journal_mode = WAL");
+
+// Create tables if they don't exist
+db.exec(`
+  CREATE TABLE IF NOT EXISTS wallets (
+    disk_id TEXT PRIMARY KEY,
+    address TEXT NOT NULL,
+    private_key TEXT NOT NULL,
+    name TEXT,
+    created_at TEXT DEFAULT CURRENT_TIMESTAMP
+  );
+
+  CREATE TABLE IF NOT EXISTS contract_state (
+    key TEXT PRIMARY KEY,
+    value TEXT
+  );
+`);
+
+function getWallet(diskId) {
+  const stmt = db.prepare("SELECT * FROM wallets WHERE disk_id = ?");
+  return stmt.get(diskId) || null;
+}
+
+function createWallet(diskId, address, privateKey, name) {
+  const stmt = db.prepare(
+    "INSERT INTO wallets (disk_id, address, private_key, name) VALUES (?, ?, ?, ?)"
+  );
+  return stmt.run(diskId, address, privateKey, name);
+}
+
+function getContractAddress() {
+  const stmt = db.prepare(
+    "SELECT value FROM contract_state WHERE key = 'contract_address'"
+  );
+  const row = stmt.get();
+  return row ? row.value : null;
+}
+
+function setContractAddress(address) {
+  const stmt = db.prepare(
+    "INSERT OR REPLACE INTO contract_state (key, value) VALUES ('contract_address', ?)"
+  );
+  return stmt.run(address);
+}
+
+function getAllWallets() {
+  const stmt = db.prepare("SELECT * FROM wallets");
+  return stmt.all();
+}
+
+module.exports = {
+  db,
+  getWallet,
+  createWallet,
+  getContractAddress,
+  setContractAddress,
+  getAllWallets,
+};