Sort activity tasks by progress

[chrisbrummel]

Summary

• Adds Progress as an Activity sort option using the gauge icon.
• Sorts queue items by download progress while keeping actively downloading tasks ahead of import-pending and other non-downloading states.
• Uses a shared progress fraction helper for task display and sorting.

Testing

• Built successfully with xcodebuild -project Ruddarr.xcodeproj -scheme Ruddarr -configuration Debug -destination id=0FEADBED-766F-4EEB-A07B-FC28167F9428 -derivedDataPath ./DerivedData-ProgressSortPR -skipPackagePluginValidation build.
• Tested in the iOS simulator with mock queue data; demo mode is not included in this branch.