Add httpOnly option to disable SSE fallback for debugging

- Added httpOnly option to UseMcpOptions to skip SSE fallback
- Updated all HTTP transport failure paths to respect httpOnly flag
- Temporarily enabled httpOnly in chat UI for streamable HTTP debugging
- Updated AGENT.md to require frequent commits after changes

examples/chat-ui/src/components/McpServerModal.tsx

@@ -23,6 +23,7 @@ function McpConnection({
     debug: true,
     autoRetry: false,
     popupFeatures: 'width=500,height=600,resizable=yes,scrollbars=yes',
+    httpOnly: true, // DEBUG: Only try HTTP transport, no SSE fallback
   })
 
   // Update parent component with connection data