Fix narrow views and crossword scroll-jump issues

Widen quiz, flashcards, practice, test, and crossword views to match the
960px max-width already used by course/lesson/assignment. Fix crossword
jumping to top on cell focus by using preventScroll and containing clue
list scrollIntoView within a max-height overflow container.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/app.js

@@ -1117,7 +1117,7 @@ async function openCrossword(itemId) {
     const key = `${r},${c}`;
     if (!cells[key]) return;
     selectCell(key);
-    cells[key].input.focus();
+    cells[key].input.focus({ preventScroll: true });
   }
 
   // Wire up cells