Revert all UI changes to prior version

The UI has been recently changed in several unannounced, unpleasant, and completely unwanted ways, all of which would benefit from being reverted to how Fandom wikis previously looked and functioned. This would restore functionality to editors and visitors, as well as Fandom's visual identity. Thus far, these changes include:

• Very rounded corners/radius-border on the page content and the right rail, unlike the previous subtle rounding
• Right rail is now semi-transparent with a blurring applied to the background image, even though themes that use a background image instead of a header are specifically designed around it NOT being visible
• New gutter/gap between the main content and the right rail, exposing a sliver of the background image (and which part is exposed changes with display dimensions)
• New collapse/widget button on the right rail that is positioned badly, has an icon of four squares (which doesn't represent anything in that rail), and is not styled to match the wiki's theme
• New "discuss" button, even when a wiki has previously expressed it does not want its pages to connect to the Discussions feature
• Other users' collections and the collection names are visible in the right rail, which abusive users could exploit
• Moving the categories to be beneath the page title and collapsing them, even when there is only a single category
• Moving the "edit" to be beneath the page title, instead of remaining in its established top-right location with its established icon
• Selecting "Edit" no longer begins an editing session, but instead requires using the dropdown menu to make a selection; depending on settings(?), this may mean dropping down "Edit" to choose between "Visual editing" or "Source editing", or dropping down "Edit" to select "Edit"
• Moving the page tools to be beneath the page title, instead of remaining in their established top-right location with their established icon of dots
• Empty vertical space/padding at the top of articles as a result of moving previous items without adjusting the padding/spacing