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

Spanakopita.cook

@@ -1,9 +1,9 @@
-image: https://roux.roo.lol/recipe-images/spanakopita.webp
 ---
 title: Skillet Spanakopita (Greek Spinach Feta Pie)
 servings: 8
 category: Greek
 source: From a Chef's Kitchen
+image: https://roux.roo.lol/recipe-images/spanakopita.webp
 ---
 
 Preheat the oven to 375 degrees.