Fix middleware example: add context parameter to call_next() (#2215)

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Jeremiah Lowin <[email protected]>

Author: jlowin

docs/servers/context.mdx

@@ -210,8 +210,8 @@ class UserAuthMiddleware(Middleware):
         # Middleware stores user info in context state
         context.fastmcp_context.set_state("user_id", "user_123")
         context.fastmcp_context.set_state("permissions", ["read", "write"])
-        
-        return await call_next()
+
+        return await call_next(context)
 
 @mcp.tool
 async def secure_operation(data: str, ctx: Context) -> str: