Chat and Settings escaped the content padding with a hardcoded
calc(100vh - 44px) height and negative margins, while Files and Social let the
whole page scroll, so secondary panes (channel list, settings nav, file tree)
scrolled away. Add a .content.flush modifier the Shell applies to the chat,
settings, files and social routes, plus a reusable .pane-scroll region, and
rework those pages to fill the content area with each pane scrolling on its
own. Removes the magic-number coupling to the topbar height.
ZacharyZhang-NY
91145fd923