As a Wikisource user, I want the ability to use subpages from all pages (rather than just those with ws-summary), so that ebook exports can more fully and accurately reflect the material that I want to download.
**Background:** At the moment, WSExport traverses pages from the user-given starting page by looking for all links to subpages, and also all links to subpages on any subpage if the link is contained within a `.ws-summary` element. This means that unless subpage ToCs are specifically marked as such, their subpages don't get included in the exported ebook.
I //think// it makes sense (although, I haven't fully looked into it) to just follow all subpage links, recursively and depth-first. This would make it easier for editors, who wouldn't have to do anything special, and readers, who would be more likely to get the whole work. There might be problems with processing works with a great many subpages, such as encyclopedias (e.g. [[ https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica | 1911 Encyclopædia Britannica]] has 36,305 subpages, and using WSExport on its top-level page at the moment does work but doesn't give a very useful ebook). I wonder if for those we'd be better off saying "this is too big" and making it obvious that although they asked for it we can't actually give the reader the entire work as an ebook.
**Acceptance Criteria:**
* Investigate the primary work that would need to be done in order to use [[ https://en.wikisource.org/wiki/Help:Subpages | subpages ]] from all pages, not just those with ws-summary, in WSExport
* Investigate the main challenges and risks associated with such work
* Provide a general estimate/idea, if possible, of the potential impact it may have on ebook export reliability
* Provide a general estimation/rough sense of the level of difficulty of effort required in doing such work