New admin UI: fonts & icons too small — add size options (small/medium/large)

Problem: Since the 2.0 admin redesign, default fonts and icons on the Feedback Board are smaller and harder to read/find: The "Category" label is hard to read, as is the sidebar text when a feedback post is open. Key action icons are very small — e.g. the Merge icon took a long time to locate, and the filter icons are tiny. Requested: Offer selectable size options for text and icons (e.g. small / medium / large, similar to OS-level accessibility settings) so admins can dial up legibility to their preference. Note: Marco confirmed a task was created to offer size options (small/medium/large) for fonts and icons, targeted for the 2.1 admin update.