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/finance/VestingWalletCliff.sol

@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v5.1.0) (finance/VestingWalletCliff.sol)
+
+pragma solidity ^0.8.20;
+
+import {SafeCast} from "../utils/math/SafeCast.sol";
+import {VestingWallet} from "./VestingWallet.sol";
+
+/**
+ * @dev Extension of {VestingWallet} that adds a cliff to the vesting schedule.
+ *
+ * _Available since v5.1._
+ */
+abstract contract VestingWalletCliff is VestingWallet {
+    using SafeCast for *;
+
+    uint64 private immutable _cliff;
+
+    /// @dev The specified cliff duration is larger than the vesting duration.
+    error InvalidCliffDuration(uint64 cliffSeconds, uint64 durationSeconds);
+
+    /**
+     * @dev Set the duration of the cliff, in seconds. The cliff starts vesting schedule (see {VestingWallet}'s
+     * constructor) and ends `cliffSeconds` later.
+     */
+    constructor(uint64 cliffSeconds) {
+        if (cliffSeconds > duration()) {
+            revert InvalidCliffDuration(cliffSeconds, duration().toUint64());
+        }
+        _cliff = start().toUint64() + cliffSeconds;
+    }
+
+    /**
+     * @dev Getter for the cliff timestamp.
+     */
+    function cliff() public view virtual returns (uint256) {
+        return _cliff;
+    }
+
+    /**
+     * @dev Virtual implementation of the vesting formula. This returns the amount vested, as a function of time, for
+     * an asset given its total historical allocation. Returns 0 if the {cliff} timestamp is not met.
+     *
+     * IMPORTANT: The cliff not only makes the schedule return 0, but it also ignores every possible side
+     * effect from calling the inherited implementation (i.e. `super._vestingSchedule`). Carefully consider
+     * this caveat if the overridden implementation of this function has any (e.g. writing to memory or reverting).
+     */
+    function _vestingSchedule(
+        uint256 totalAllocation,
+        uint64 timestamp
+    ) internal view virtual override returns (uint256) {
+        return timestamp < cliff() ? 0 : super._vestingSchedule(totalAllocation, timestamp);
+    }
+}