Randomize questions on every Anki regen

Also make explanation section slightly more readable

EXPLANATIONS.md

@@ -82,7 +82,7 @@ modify Python code to ship a new explanation. End-to-end:
    inline `$...$` LaTeX rewritten to MathJax `\(...\)`, same as the
    question text), and a "Source: ..." line.
 3. The block lands inside `.af-back` at the very end, styled by the
-   `.af-explanation*` CSS rules — serif italic body, sans-serif
+   `.af-explanation*` CSS rules — serif body, sans-serif
    metadata, separated from the answer by a top border. When the
    entry's `confidence` is **below 7**, a small "low confidence"
    badge appears next to the **Explanation** header — a hint to the