School drop-off. Doctor’s appointments. The grocery list. That thing you forgot to sign. Here’s how to pick an iPad planner that holds all of it — without becoming one more thing to manage. There’s a particular kind of mental load that doesn’t show up in any productivity book. It’s the invisible spreadsheet running in the back of your head at all times: what’s for dinner, who needs to be where, when the permission slip is due, which kid has soccer…