- Each `DirectoryDropdown` now remembers the longest/most-recent path (navigating with keys).
- Separated mouse and keyboard directory dropdown selection.
- Clicking, scrolling and tapping no longer dismiss directory dropdowns.
- Added a small border on the left on the keyboard-highlighted dropdown selection.
- Fixed bug with dropdown scrolling with Model Info View.
- Encapsulated model directories formally in new `ModelDirectories` data structure.
- Moved download button in the Download Tab.
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