AO3-3764 Paginate tag set nominations review page

[pmonfort]

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• Have you added tests for any changed functionality?
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Issue

https://otwarchive.atlassian.net/browse/AO3-3764

Purpose

When a tag set has more than 30 unreviewed nominations, moderators currently see a random subset with the message "There are too many nominations to show at once." This makes it impossible to systematically review all nominations.

This PR replaces the random selection with proper pagination using pagy:

• Paginate nominations by unique tagname, grouping duplicates (same tag nominated by multiple users) into a single entry
• Each tag type (fandom, character, relationship, freeform) paginates independently with its own page param
• Heading shows "X - Y of Z [Type]" when paginated, or "[Type] (N left to review)" when everything fits on one page
• Pagination links include anchors to scroll to the correct fieldset
• Order by created_at ascending for deterministic results
• Removed the random selection logic and the "too many nominations" flash message

Testing Instructions

1. Log in as a moderator of a tag set with more than 25 unreviewed nominations
2. Go to Review Nominations
3. Verify pagination links appear and each tag type paginates independently
4. Verify that navigating pages does not affect other tag types (e.g. going to fandom page 2 keeps freeform on page 1)
5. Verify duplicate nominations (same tagname from different users) appear only once
6. Verify approving/rejecting tags updates counts correctly
7. Verify tag sets with fewer than 25 nominations show no pagination links and display the "(N left to review)" heading
8. Verify the old "There are too many nominations to show at once" message no longer appears

Credit

Pablo Monfort (he/him)

[sarken]

Question! Does the anchor_string here mean that the pagination links should be like ?fandom_page=3#fandom_nominations?

I swear I saw that behavior when I first pulled this code to try it out, but it has disappeared on me, so I'm confused. 😆

[pmonfort]

Yes, that's the intended behavior! The anchor_string parameter name is a bit misleading, it refers to the HTML anchor element ( tag) not URL anchors/fragments. I've pushed a fix using the correct fragment parameter.
Good catch! Thanks!

[sarken]

Just a couple of nitpicks/questions about the tests! Aside from that, this looks good and I'm excited. 🎉

[sarken]

Just one last question!

[sarken]

I might be missing something here. How does this tell us these are definitely the unique tagnames for page 3 and not the same tags from page 1 or 2? (It's okay if it doesn't. In my opinion, we can remove it instead of expanding it, since the test above already demonstrates the tagnames are unique. If we do that, it might also mean we can go from noms_per_page * 3 to 2.)

[pmonfort]

Make sense, 2 pages is enough to validate what we need.

[sarken]

🎉