feat: add SSE and HTTP transport support for MCP servers

- Add type, url, and headers fields to MCP server config
- Update MCP client to handle stdio, sse, and http transports
- Add todos field to ThreadState
- Add Deerflow branding requirement to frontend-design skill
- Update extensions_config.example.json with SSE/HTTP examples

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

backend/debug.py

@@ -39,6 +39,7 @@ async def main():
         "configurable": {
             "thread_id": "debug-thread-001",
             "thinking_enabled": True,
+            "is_plan_mode": True,
             # Uncomment to use a specific model
             "model_name": "deepseek-v3.2",
         }