Add title to serverInfo

Follow-up to #109.

`title` has also been added to `serverInfo` and `clientInfo` by
https://github.com/modelcontextprotocol/modelcontextprotocol/pull/663.

Since `clientInfo` is not treated as product code, support is implemented only in `serverInfo`.

See also https://modelcontextprotocol.io/specification/2025-06-18/schema#implementation.

test/mcp/server_test.rb

@@ -69,6 +69,7 @@ module MCP
 
       @server = Server.new(
         name: @server_name,
+        title: "Example Server Display Name",
         version: "1.2.3",
         instructions: "Optional instructions for the client",
         tools: [@tool, @tool_that_raises],
@@ -140,6 +141,7 @@ module MCP
           },
           serverInfo: {
             name: @server_name,
+            title: "Example Server Display Name",
             version: "1.2.3",
           },
           instructions: "Optional instructions for the client",
@@ -769,6 +771,18 @@ module MCP
       assert_equal Configuration::DEFAULT_PROTOCOL_VERSION, response[:result][:protocolVersion]
     end
 
+    test "server uses default title when not configured" do
+      server = Server.new(name: "test_server")
+      request = {
+        jsonrpc: "2.0",
+        method: "initialize",
+        id: 1,
+      }
+
+      response = server.handle(request)
+      assert_nil response[:result][:serverInfo][:title]
+    end
+
     test "server uses default version when not configured" do
       server = Server.new(name: "test_server")
       request = {