fix: correct YAML frontmatter, convert images to proper WebP format

- Moved image: field from outside to inside YAML frontmatter (50 files)
- Converted all 56 non-WebP images to proper WebP format via ImageMagick
- Fixed Python shebangs for portability
- Updated source fields in 2 Task 3 recipes

Black Bean and Corn Salad.cook

@@ -1,4 +1,3 @@
-image: https://roux.roo.lol/recipe-images/black-bean-and-corn-salad.webp
 ---
 title: Black Bean and Corn Salad
 servings: 4
@@ -13,6 +12,7 @@ tags:
   - avocado
   - summer
   - healthy
+image: https://roux.roo.lol/recipe-images/black-bean-and-corn-salad.webp
 ---
 
 In a large #mixing bowl{}, whisk together the @lime juice{1/4%cup}, @avocado oil{3%tablespoons}, @garlic{1%clove}, grated, @cumin{1/2%teaspoon}, @sea salt{3/4%teaspoon}, and @black pepper{}.