fix: pass req.body to handleRequest for proper MCP protocol handling

The StreamableHTTPServerTransport.handleRequest() method requires the parsed
body as the third argument for POST requests. This was causing "Parse error:
Invalid JSON" responses for all MCP requests.

src/index.ts

@@ -110,9 +110,9 @@ class OpenRouterMultimodalServer {
           return;
         }
 
-        // Let the transport handle the SSE stream
+        // Let the transport handle the SSE stream (no body for GET)
         const transport = transports[sessionId];
-        await transport.handleRequest(req, res);
+        await transport.handleRequest(req, res, undefined);
         return;
       }
 
@@ -174,9 +174,9 @@ class OpenRouterMultimodalServer {
         transport = transports[sessionId];
       }
 
-      // Handle the request
+      // Handle the request - pass body for POST, omit for GET/DELETE
       try {
-        await transport.handleRequest(req, res);
+        await transport.handleRequest(req, res, req.body);
       } catch (error) {
         console.error('[MCP] Request handling error:', error);
         if (!res.headersSent) {