🐛 Reordering product categories fails when hidden categories exist

[LogFlames]

Describe the bug

Reordering product categories via POST /events/{event_id}/products/sort fails with "The ordered category IDs must exactly match all categories for the event without missing or extra IDs." even when all category IDs from GET /events/{event_id}/product-categories are included.

The root cause is a mismatch between the two endpoints:

• GET /product-categories filters out categories where is_hidden = true via ProductFilterService::filter() (GetProductCategoriesHandler.php)
• SortProductsHandler loads all categories (including hidden) from the DB and requires an exact set match (SortProductsHandler.php#L36-L40)

Since the client never receives hidden category IDs, it's impossible to include them in the sort request.

To Reproduce

1. Create an event with at least one product category where is_hidden = true
2. Open the event's product management page
3. Try to reorder product categories via drag & drop
4. The sort request fails with the error above

Expected behavior

Reordering should succeed. Hidden categories should either be excluded from the sort handler's validation check, or the listing endpoint should expose them to organizer-facing callers.

Suggested fix

Show hidden categories in admin panel to allow reordering them (and make "hidden" mean hidden for the consumer).

[Viburnum]

@LogFlames Shouldn't the hidden categories be visible in manage/admin view and only hidden for the customer?
Because I just stumpled upon the issue, while creating a category for guest-list related tickets, which I want to hide for the customer and manually create tickets in the attendee manager view.

[LogFlames]

@Viburnum that sounds more reasonable, I agree. Otherwise, it would just be another version of deleting the categories. I have updated my suggested fix.

[Viburnum]

I added a PR #1138