Fix border radius for file comment header

Chad Lavimoniererequested to merge
20250911-clavimoniere-discussion-file-comment-border-fix into master

What does this MR do and why?

Ensure that the file title holder for a comment on a file does not have rounded bottom corners.

Also fixes bottom corner problems for note content in dark mode (the note content td does not need its own background color, as every child supplies its own background color)

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Before After
Screenshot_2025-09-11_at_15.28.55 Screenshot_2025-09-11_at_15.47.38

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