citizen: implement Implement: Defines the interface for the Greeter contract

contracts/interfaces/IGreeter.sol

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.19;
+
+/**
+ * @title IGreeter
+ * @dev Interface for the Greeter contract defining core interaction methods
+ */
+interface IGreeter {
+    /// @notice Emitted when a greeting is updated
+    event GreetingChanged(address indexed updater, string newGreeting);
+
+    /// @notice Thrown when an unauthorized address attempts to modify the greeting
+    error UnauthorizedGreetingModification(address caller);
+
+    /**
+     * @notice Retrieves the current stored greeting
+     * @return The current greeting string
+     */
+    function getGreeting() external view returns (string memory);
+
+    /**
+     * @notice Updates the greeting with optional authorization checks
+     * @param newGreeting The new greeting message to set
+     * @param nonce A unique transaction identifier to prevent replay attacks
+     * @param signature Optional cryptographic signature for advanced authorization
+     */
+    function updateGreeting(
+        string calldata newGreeting, 
+        uint256 nonce, 
+        bytes calldata signature
+    ) external;
+
+    /**
+     * @notice Checks if an address has greeting modification permissions
+     * @param account The address to check for authorization
+     * @return Boolean indicating whether the address can modify greetings
+     */
+    function isAuthorizedGreeter(address account) external view returns (bool);
+
+    /**
+     * @notice Retrieves the contract's creation timestamp
+     * @return The block timestamp when the contract was deployed
+     */
+    function getDeploymentTimestamp() external view returns (uint256);
+}