Make the Read Receipts dialog scrollable again

[Septicity]

Description

At some point between commits 43cb531 and f4cc4d5, in the process of switching various UI elements into unified modals, the read receipts modal (specifically the one that opens from an individual message's context menu) lost its ability to be scrolled through.

In this patch, I've reverted that specific component to its old form, both to immediately return the functionality and to provide a useful reference state for the process of creating a more polished fix.

I recommend directly patching this pull request to properly unify the modals first, but it should be functional enough on its own to be implemented as an immediate fix if you prefer.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

AI disclosure:

• Partially AI assisted (clarify which code was AI assisted and briefly explain what it does).
• Fully AI generated (explain what all the generated code does in moderate detail).

[Septicity]

Looks like some jank from merging the old code made it through, as well as some linter troubles...