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

Dried Fava Soup.cook

@@ -1,4 +1,3 @@
-image: https://roux.roo.lol/recipe-images/dried-fava-soup.webp
 ---
 title: Dried Fava Soup with Mint and Guajillo Chiles
 prep_time: 10 minutes
@@ -12,6 +11,7 @@ tags:
   - soup
 description: A slow-simmered dried fava bean soup with roasted tomatoes, garlic, and onion, finished with mint and cilantro and topped with a tangy quick-pickled guajillo chile mixture.
 source: 101 Cookbooks (adapted from Rick Bayless’s Mexican Kitchen)
+image: https://roux.roo.lol/recipe-images/dried-fava-soup.webp
 ---
 
 Make sure the @hulled dried fava bean{1%lb} are clean and free of dirt, then rinse them well.