[Feature Request] Add an action to mark a puzzle as duplicate

We have some puzzles that are kinda duplicated (similar content but for the same method). These are from before "cloning" was a feature.

We have the filter to hide cloned puzzles but then some puzzles are similar to others but not hidden, and we can end up sharing really similar puzzles too close to each other.

It would be great to have an option to mark a puzzle as a duplicate of another puzzle, so we can filter them out too when looking for things to clone to avoid this.

The idea would be to have a new "duplicated" or "duplicated_puzzle_id" column and a way to mark a puzzle as a duplicate of another puzzle (I imagine the button in the UI opens a popup to input the id of the other puzzle), and then have a new filter to hide duplicated puzzles.

This should only be done on one of the puzzles when there's a duplication, so one does not get hidden when filtering things out.

Start with the existing cloning filter and puzzle UI, then trace how puzzle attributes are stored and filtered. Define the duplicate column and the UI action or popup for entering another puzzle ID, and verify that filtering hides only the puzzle marked as duplicated while leaving its original visible.

Written by the indexing model from the issue text.