Feature summary (what you would like to be able to do and where):
Drop page numbers from the reference list in Re-use tab of Add a citation dialog. Then when user selects a reference for re-use, pop-up dialog to enter the page number, and save

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Currently the reference list includes previously entered page numbers. This is only relevant for repeatedly citing the same page numbers in a source. If instead the user wants to reference different pages, which is typically the much more common case, they have to switch to source edit, and use something like sfn, which is a pain. Or they can for example go back to automatic, re-enter a link from example Google books of the same source to create a citation with the new page number. This too requires the extra step of re-entering the source, plus it often results in multiple references to the same source in the reference list, each with different page numbers, extra code in the articles, etc. Sometimes to get around this I also cite page numbers of entire chapters, if I know I will reference multiple different pages in that chapter, often people skip citing pages completely, etc.

Benefits (why should this be implemented?):
Citing sources is the single biggest pain point of writing articles, resulting frequently in too few inline citations in many articles, missing pages in citations, probably also discouraging some from editing. Re-use of citations can be very beneficial, but the current re-use feature has problems, limiting its use, no doubt particularly among new users who may be unfamiliar with wikitext and features like sfn. The proposed change can save users time and effort, and thus also encourage more editing