chore: improve the FFG comparison table for ebooks (playfulprogramming#1121)

This PR updates the FFG ebook to use 3 columns instead of 4 for spacing
constraints and readability:


![image](https://github.com/user-attachments/assets/0d4fdef5-6c9d-4c29-83c3-abd2e87b3bd5)

Author: crutchcorn

build-scripts/epubs/generate-epubs.ts

@@ -181,7 +181,7 @@ async function generateCollectionEPub(
 			author: authors,
 			publisher: "Unicorn Utterances",
 			cover: collection.coverImgMeta.absoluteFSPath,
-			allowedAttributes: [...defaultAllowedAttributes, "start"],
+			allowedAttributes: [...defaultAllowedAttributes, "start", "colSpan"],
 			css: await fs.readFile(resolve(__dirname, "./epub.css"), "utf-8"),
 			// fonts: ['/path/to/Merriweather.ttf'],
 			lang: "en",