feat(gateway): add MCP server endpoint with streamable HTTP transport (#137)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/src/mcp/mcp.dto.ts

@@ -0,0 +1,19 @@
+/**
+ * MCP (Model Context Protocol) DTOs
+ *
+ * Defines the data transfer objects for the MCP streamable HTTP transport.
+ * See: https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http
+ */
+
+export interface McpToolDescriptor {
+  name: string;
+  description: string;
+  inputSchema: Record<string, unknown>;
+}
+
+export interface McpServerInfo {
+  name: string;
+  version: string;
+  protocolVersion: string;
+  tools: McpToolDescriptor[];
+}