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/contracts/AfterCoin.sol

@@ -0,0 +1,183 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.20;
+
+/**
+ * @title AfterCoin (AFC)
+ * @notice ERC-20 token for the Afterlife Project game preservation platform.
+ *         1 AFC = 1 diamond. Zero decimals — integer-only balances.
+ * @dev Self-contained implementation (no OpenZeppelin). Owner-gated mint,
+ *      burn-from, and bridge-transfer helpers for the off-chain bridge service.
+ */
+contract AfterCoin {
+
+    // ──────────────────────────── ERC-20 metadata ────────────────────────────
+
+    string private constant _name   = "AfterCoin";
+    string private constant _symbol = "AFC";
+    uint8  private constant _decimals = 0;   // 1 token = 1 diamond
+
+    // ──────────────────────────── State ──────────────────────────────────────
+
+    uint256 private _totalSupply;
+
+    mapping(address => uint256)                     private _balances;
+    mapping(address => mapping(address => uint256)) private _allowances;
+
+    address public owner;
+
+    // ──────────────────────────── Events (ERC-20) ────────────────────────────
+
+    event Transfer(address indexed from, address indexed to, uint256 value);
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+
+    // ──────────────────────────── Errors ─────────────────────────────────────
+
+    error NotOwner();
+    error ZeroAddress();
+    error InsufficientBalance(address account, uint256 required, uint256 available);
+    error InsufficientAllowance(address spender, uint256 required, uint256 available);
+
+    // ──────────────────────────── Modifier ───────────────────────────────────
+
+    modifier onlyOwner() {
+        if (msg.sender != owner) revert NotOwner();
+        _;
+    }
+
+    // ──────────────────────────── Constructor ────────────────────────────────
+
+    constructor() {
+        owner = msg.sender;
+        // Initial supply is 0 — tokens are minted on demand by the bridge.
+    }
+
+    // ──────────────────────────── ERC-20 view functions ──────────────────────
+
+    function name() external pure returns (string memory) {
+        return _name;
+    }
+
+    function symbol() external pure returns (string memory) {
+        return _symbol;
+    }
+
+    function decimals() external pure returns (uint8) {
+        return _decimals;
+    }
+
+    function totalSupply() external view returns (uint256) {
+        return _totalSupply;
+    }
+
+    function balanceOf(address account) external view returns (uint256) {
+        return _balances[account];
+    }
+
+    function allowance(address tokenOwner, address spender) external view returns (uint256) {
+        return _allowances[tokenOwner][spender];
+    }
+
+    // ──────────────────────────── ERC-20 mutative functions ──────────────────
+
+    function transfer(address to, uint256 amount) external returns (bool) {
+        _transfer(msg.sender, to, amount);
+        return true;
+    }
+
+    function approve(address spender, uint256 amount) external returns (bool) {
+        _approve(msg.sender, spender, amount);
+        return true;
+    }
+
+    function transferFrom(
+        address from,
+        address to,
+        uint256 amount
+    ) external returns (bool) {
+        uint256 currentAllowance = _allowances[from][msg.sender];
+        if (currentAllowance != type(uint256).max) {
+            if (currentAllowance < amount) {
+                revert InsufficientAllowance(msg.sender, amount, currentAllowance);
+            }
+            unchecked {
+                _approve(from, msg.sender, currentAllowance - amount);
+            }
+        }
+        _transfer(from, to, amount);
+        return true;
+    }
+
+    // ──────────────────────────── Owner-only functions ───────────────────────
+
+    /**
+     * @notice Mint new tokens to `to`. Only callable by the contract owner.
+     * @param to   Recipient address.
+     * @param amount Number of tokens to create.
+     */
+    function mint(address to, uint256 amount) external onlyOwner {
+        if (to == address(0)) revert ZeroAddress();
+        _totalSupply += amount;
+        _balances[to] += amount;
+        emit Transfer(address(0), to, amount);
+    }
+
+    /**
+     * @notice Burn tokens from `from`. Only callable by the contract owner.
+     *         Does NOT require an allowance — the owner is the bridge operator.
+     * @param from   Address whose tokens are burned.
+     * @param amount Number of tokens to destroy.
+     */
+    function burnFrom(address from, uint256 amount) external onlyOwner {
+        if (from == address(0)) revert ZeroAddress();
+        uint256 bal = _balances[from];
+        if (bal < amount) {
+            revert InsufficientBalance(from, amount, bal);
+        }
+        unchecked {
+            _balances[from] = bal - amount;
+        }
+        _totalSupply -= amount;
+        emit Transfer(from, address(0), amount);
+    }
+
+    /**
+     * @notice Transfer tokens between two addresses on behalf of the bridge.
+     *         Only callable by the contract owner.
+     * @param from   Source address.
+     * @param to     Destination address.
+     * @param amount Number of tokens to move.
+     */
+    function bridgeTransfer(
+        address from,
+        address to,
+        uint256 amount
+    ) external onlyOwner {
+        _transfer(from, to, amount);
+    }
+
+    // ──────────────────────────── Internal helpers ───────────────────────────
+
+    function _transfer(address from, address to, uint256 amount) internal {
+        if (from == address(0)) revert ZeroAddress();
+        if (to == address(0)) revert ZeroAddress();
+
+        uint256 fromBal = _balances[from];
+        if (fromBal < amount) {
+            revert InsufficientBalance(from, amount, fromBal);
+        }
+        unchecked {
+            _balances[from] = fromBal - amount;
+        }
+        _balances[to] += amount;
+
+        emit Transfer(from, to, amount);
+    }
+
+    function _approve(address tokenOwner, address spender, uint256 amount) internal {
+        if (tokenOwner == address(0)) revert ZeroAddress();
+        if (spender == address(0)) revert ZeroAddress();
+
+        _allowances[tokenOwner][spender] = amount;
+        emit Approval(tokenOwner, spender, amount);
+    }
+}