Fix JsonRpc\Error id parameter (expects int|string, not null)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mowens3

src/ErrorBag.php

@@ -287,7 +287,7 @@ public function toJsonRpcError(): object
         unset($data['success'], $data['error']);
 
         return new \Mcp\Schema\JsonRpc\Error(
-            null, // JSON-RPC request ID (null for notifications/errors)
+            0, // JSON-RPC request ID (0 as placeholder when ID unknown)
             $primary->getJsonRpcCode(),
             $this->getSummaryMessage(),
             $data

src/McpError.php

@@ -384,7 +384,7 @@ public function toJsonRpcError(): object
         unset($data['success'], $data['error']);
 
         return new \Mcp\Schema\JsonRpc\Error(
-            null, // JSON-RPC request ID (null for notifications/errors)
+            0, // JSON-RPC request ID (0 as placeholder when ID unknown)
             $this->getJsonRpcCode(),
             $this->getMessage(),
             empty($data) ? null : $data