Add option to keep selection when clearing search

[Ahelsamahy]

Summary

Add option to keep selection when clearing search

Today, when search is cleared, Maccy always jumps selection back to the first unpinned item.
With this change, users can enable a setting to keep the previously selected item instead.

Problem

My common workflow is:

1. I copy two items. A and B
2. I forget what is item B but I still remember what is A.
3. I Search for item A hoping that I find B
4. I search for A in clipboard. I find it.
5. Clear search to continue around that same position and find nearby item B.

Current behavior resets selection to the top.

Changes

• Added new default key:
• preserveSelectionAfterSearch (default: false)
• Added new setting in General → Search:
• Keep selected item when clearing search
• Updated search-clear behavior in History.searchQuery.didSet:
• If enabled and previous selection is still visible, keep that selection.
• Otherwise fallback to existing behavior (select first unpinned item).
• Added tests in HistoryTests for:
• default behavior (jump to top)
• enabled behavior (preserve selection)

Backward compatibility

• Default value is false, so existing behavior is unchanged unless users enable it.

Testing

• Build passes with:
• xcodebuild build -project Maccy.xcodeproj -scheme Maccy -configuration Release -destination 'platform=macOS' CODE_SIGNING_ALLOWED=NO CODE_SIGNING_REQUIRED=NO
• Added unit tests in HistoryTests for new behavior.

I couldn't find a way to know how to run the changes locally. I came up with these

  cd /Maccy

  # Build Release (unsigned)
  xcodebuild build \
    -project Maccy.xcodeproj \
    -scheme Maccy \
    -configuration Release \
    -destination 'platform=macOS' \
    CODE_SIGNING_ALLOWED=NO CODE_SIGNING_REQUIRED=NO

  # Find built app
  APP_PATH="$(find ~/Library/Developer/Xcode/DerivedData -path '*Maccy*/Build/Products/Release/Maccy.app' | tail -n 1)"
  echo "$APP_PATH"

  # Replace installed app
  pkill Maccy || true
  rm -rf /Applications/Maccy.app
  cp -R "$APP_PATH" /Applications/Maccy.app

  # Remove quarantine + launch
  xattr -dr com.apple.quarantine /Applications/Maccy.app
  open /Applications/Maccy.app

Notes

• Only English settings strings were added in this PR for the new option label/tooltip.