Some polish, nice to have new features and lots of little fixes, including some error handling for bad inputs (Looking at you, Andrew!)
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- Fixed a crash when entering invalid characters into a conversion field
- Invalid input now reverts to the last valid value with an on-screen message
- Rejected malformed or ambiguous comma-grouped numbers (e.g. "1,2,3") instead of silently ignoring them
- Settings' category picker now stays in sync with whatever category you're actively converting, instead of always defaulting to the first one
- Added a "Reset order" button (with a confirm/cancel prompt) to restore a category's default unit order in Settings, withour affecting show/hide settings.
- Sped up the long-press needed to start dragging a unit in the settings menu
- Added long-press tooltips that show each unit's full name