Spanish Shrimp and Rice with Saffron Mayo

Name: Spanish Shrimp and Rice with Saffron Mayo
Ingredients: 1 cup bomba, arborio, or carnaroli rice; 1 lb. shrimp, peeled, tails left on, deveined, patted dry; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, plus more; Freshly ground pepper; ½ cup store-bought marinara sauce (such as Rao’s or Mutti); 2 Tbsp. extra-virgin olive oil; 6 garlic cloves, thinly sliced; ½ cup coarsely chopped roasted red peppers from a jar; 1 tsp. ground cumin; 2 pinches of saffron threads, divided; ¼ cup sherry vinegar or red wine vinegar; ½ cup mayonnaise; Sliced Peppadew peppers in brine and chopped parsley (for serving)