Add RewardsManager for pool units sync

Why:
Create minimal manager to mirror ERC-4626 asset balances to
Superfluid pool units.

Test plan:
- bunx hardhat compile
- bunx hardhat test test/rewards.manager.test.ts

Author: youngkidwarrior

contracts/rewards/RewardsManager.sol

@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.28;
+
+// Rule 3 note:
+// This contract mirrors the minimal pattern described in Superfluid's Distribution Pools (GDA) docs
+// for updating pool units to match an external ERC-20 balance source. We avoid novel patterns and
+// only include functions we can mirror from examples. Pool creation is left to scripts (admin = this),
+// keeping on-chain logic minimal and example-aligned.
+//
+// References:
+// - Pools/GDA guide: https://docs.superfluid.org/docs/protocol/distributions/guides/pools
+// - Example operations: updateMemberUnits(member, units)
+// - We intentionally do not embed SuperTokenV1Library usage here to avoid guessing signatures.
+//   A deploy script will create the pool with this contract as admin, then pass the pool address.
+
+import {AccessControl} from "@openzeppelin/contracts/access/AccessControl.sol";
+import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+import {SafeCast} from "@openzeppelin/contracts/utils/math/SafeCast.sol";
+
+interface ISuperfluidPool {
+    // Mirrors the method name from Superfluid pool examples; return value (if any) is ignored.
+    function updateMemberUnits(address member, uint128 units) external;
+}
+
+/// @title RewardsManager
+/// @notice Mirrors ERC-4626 share balances into Superfluid Pool units (1:1, cast to uint128).
+///         Pool is expected to be created with this contract as admin by an external script.
+contract RewardsManager is AccessControl {
+    using SafeCast for uint256;
+
+    /// @dev Super Token used as the pool payout asset (SENDx). Stored for reference/logging only in this phase.
+    address public immutable sendx;
+
+    /// @dev ERC-20 share token (ERC-4626 shares) whose balances define pool units.
+    IERC20 public immutable shareToken;
+
+    /// @dev Superfluid pool to update units on.
+    ISuperfluidPool public immutable pool;
+
+    event Synced(address indexed who, uint128 units);
+
+    constructor(address _sendx, address _shareToken, address _pool, address admin) {
+        require(_sendx != address(0), "sendx");
+        require(_shareToken != address(0), "share");
+        require(_pool != address(0), "pool");
+        require(admin != address(0), "admin");
+        sendx = _sendx;
+        shareToken = IERC20(_shareToken);
+        pool = ISuperfluidPool(_pool);
+        _grantRole(DEFAULT_ADMIN_ROLE, admin);
+    }
+
+    /// @notice Set pool units for `who` to their current share balance (cast to uint128).
+    /// @dev Open to anyone; cannot arbitrarily set units — only mirrors on-chain share balance.
+    function sync(address who) public {
+        require(who != address(0), "zero");
+        uint256 bal = shareToken.balanceOf(who);
+        uint128 units = bal.toUint128();
+        pool.updateMemberUnits(who, units);
+        emit Synced(who, units);
+    }
+
+    /// @notice Batch variant of sync.
+    function batchSync(address[] calldata who) external {
+        uint256 n = who.length;
+        for (uint256 i = 0; i < n; i++) {
+            sync(who[i]);
+        }
+    }
+}