[RTE] Edit icon overflows container when text line is too long

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Observed behavior

When the question field's Rich Text Editor (RTE) contains a long, unbroken line of text (no spaces or word-wrap opportunities), the edit (pencil) icon overflows outside the right boundary of the RTE container and renders floating to the right of it.

Expected behavior

The edit icon should not escape the RTE container when content overflows. The correct behavior is TBD — either the icon floats on top of the content (with a background) or remains fully contained within the box — but in either case it should not render outside the container boundary.

User-facing consequences

Content creators building exercises in Studio see a broken layout when entering long, unbroken text in a question field — the edit icon renders outside the RTE container, making the assessment editor look visually incorrect.

Steps to reproduce

1. Create a new exercise node in Studio.
2. Add a question.
3. In the question field, type a long string of text with no spaces or word breaks (e.g., TestestestTestestest... repeated many times).
4. Observe that the edit (pencil) icon overflows outside the right boundary of the RTE container.

AI usage

Used Claude to help draft this issue from a description and screenshot. Reviewed and confirmed all sections for accuracy.