Area Highlighting When Replying to Comments in Proofs

[#1]

Description:
Allow users to highlight areas in a proof when replying to comments, not just when creating new ones.

Importance:
Stakeholders often miss highlighting content or only mark part of what's relevant. This would improve clarity and streamline review workflows.

How it could work:
When replying to a comment in a proof, users should have the option to create a new highlight linked to their reply.

Current Behaviour:
Highlighting is only available when adding a new comment, not when replying to an existing one.