refactor: move brother_node development artifact to dev/test-nodes subdirectory

Development Artifact Cleanup:
✅ BROTHER_NODE REORGANIZATION: Moved development test node to appropriate location
- dev/test-nodes/brother_node/: Moved from root directory for better organization
- Contains development configuration, test logs, and test chain data
- No impact on production systems - purely development/testing artifact

✅ DEVELOPMENT ARTIFACTS IDENTIFIED:
- Chain ID: aitbc-brother-chain (test/development chain)
- Ports: 8010 (P2P) and 8011 (RPC) - different from production
- Environment: .env file with test configuration
- Logs: rpc.log and node.log from development testing session (March 15, 2026)

✅ ROOT DIRECTORY CLEANUP: Removed development clutter from production directory
- brother_node/ moved to dev/test-nodes/brother_node/
- Root directory now contains only production-ready components
- Development artifacts properly organized in dev/ subdirectory

DIRECTORY STRUCTURE IMPROVEMENT:
📁 dev/test-nodes/: Development and testing node configurations
🏗️ Root Directory: Clean production structure with only essential components
🧪 Development Isolation: Test environments separated from production

BENEFITS:
✅ Clean Production Directory: No development artifacts in root
✅ Better Organization: Development nodes grouped in dev/ subdirectory
✅ Clear Separation: Production vs development environments clearly distinguished
✅ Maintainability: Easier to identify and manage development components

RESULT: Successfully moved brother_node development artifact to dev/test-nodes/ subdirectory, cleaning up the root directory while preserving development testing environment for future use.

dev/env/node_modules/@openzeppelin/contracts/account/extensions/draft-ERC7821.sol

@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v5.4.0) (account/extensions/draft-ERC7821.sol)
+
+pragma solidity ^0.8.20;
+
+import {ERC7579Utils, Mode, CallType, ExecType, ModeSelector} from "../utils/draft-ERC7579Utils.sol";
+import {IERC7821} from "../../interfaces/draft-IERC7821.sol";
+import {Account} from "../Account.sol";
+
+/**
+ * @dev Minimal batch executor following ERC-7821.
+ *
+ * Only supports supports single batch mode (`0x01000000000000000000`). Does not support optional "opData".
+ *
+ * @custom:stateless
+ */
+abstract contract ERC7821 is IERC7821 {
+    using ERC7579Utils for *;
+
+    error UnsupportedExecutionMode();
+
+    /**
+     * @dev Executes the calls in `executionData` with no optional `opData` support.
+     *
+     * NOTE: Access to this function is controlled by {_erc7821AuthorizedExecutor}. Changing access permissions, for
+     * example to approve calls by the ERC-4337 entrypoint, should be implemented by overriding it.
+     *
+     * Reverts and bubbles up error if any call fails.
+     */
+    function execute(bytes32 mode, bytes calldata executionData) public payable virtual {
+        if (!_erc7821AuthorizedExecutor(msg.sender, mode, executionData))
+            revert Account.AccountUnauthorized(msg.sender);
+        if (!supportsExecutionMode(mode)) revert UnsupportedExecutionMode();
+        executionData.execBatch(ERC7579Utils.EXECTYPE_DEFAULT);
+    }
+
+    /// @inheritdoc IERC7821
+    function supportsExecutionMode(bytes32 mode) public view virtual returns (bool result) {
+        (CallType callType, ExecType execType, ModeSelector modeSelector, ) = Mode.wrap(mode).decodeMode();
+        return
+            callType == ERC7579Utils.CALLTYPE_BATCH &&
+            execType == ERC7579Utils.EXECTYPE_DEFAULT &&
+            modeSelector == ModeSelector.wrap(0x00000000);
+    }
+
+    /**
+     * @dev Access control mechanism for the {execute} function.
+     * By default, only the contract itself is allowed to execute.
+     *
+     * Override this function to implement custom access control, for example to allow the
+     * ERC-4337 entrypoint to execute.
+     *
+     * ```solidity
+     * function _erc7821AuthorizedExecutor(
+     *   address caller,
+     *   bytes32 mode,
+     *   bytes calldata executionData
+     * ) internal view virtual override returns (bool) {
+     *   return caller == address(entryPoint()) || super._erc7821AuthorizedExecutor(caller, mode, executionData);
+     * }
+     * ```
+     */
+    function _erc7821AuthorizedExecutor(
+        address caller,
+        bytes32 /* mode */,
+        bytes calldata /* executionData */
+    ) internal view virtual returns (bool) {
+        return caller == address(this);
+    }
+}