Pinterest’s newest ad starts with two young women doomscrolling in the dark. It’s a familiar nightly ritual for millions. As one of them slumps on the bed in a Reels-induced semicoma, the other gets an idea and opens . . . you guessed it, Pinterest. Suddenly, an energetic dance track fills the room, and the two are inspired to get their best ’fits together for a night out. It ends with the tagline, “The best thing you can find online is a reason…