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

Asparagus Salad.cook

@@ -1,4 +1,3 @@
-image: https://roux.roo.lol/recipe-images/asparagus-salad.webp
 ---
 title: Asparagus Salad
 prep_time: 20 minutes
@@ -11,6 +10,7 @@ tags:
   - salad
 description: A fresh spring asparagus salad with peas, radishes, feta, pine nuts, and herbs, tossed with lemon and olive oil and finished with creamy avocado dressing.
 source: Love and Lemons
+image: https://roux.roo.lol/recipe-images/asparagus-salad.webp
 ---
 
 Bring a large #pot of well-salted @water{} to a boil and prepare a #bowl of @ice water{}.