Add recipe favorites and serving scaling

[itsDNNS]

Summary

• Add recipe favorites and a recently used marker after pushing ingredients to shopping
• Add serving scaling in the recipe editor so ingredient amounts can be adjusted before saving
• Cover the new behavior with backend, frontend, and browser tests

Test plan

• DATABASE_URL=sqlite:///./test-recipes.db JWT_SECRET=test-secret PYTHONPATH=$PWD pytest -q tests/test_recipes.py tests/test_recipe_qol.py tests/test_meal_plans.py
• npm test -- --runTestsByPath __tests__/lib/recipes.test.js __tests__/components/RecipesView.test.js --runInBand --silent=false
• BACKEND_URL=http://127.0.0.1:8000 npm run build
• npx playwright test e2e/tests/recipes.spec.js --project='Desktop Chrome' --reporter=list
• npx playwright test e2e/tests/recipes.spec.js --project='Mobile Chrome' --reporter=list

Closes #234