Set minimum width

[matthew-white]

We know that Frontend doesn't work particularly well on mobile (#271). We've decided not to prioritize the mobile experience, but we could prevent unexpected behavior on mobile by setting a minimum width for Frontend. That would prevent overlapping elements or content overflow, for example. By setting a minimum width, the user would need to scroll horizontally on mobile to see content on the righthand side of the page.

@issa-tseng designs for a width of 1000px, so we could use that for the minimum width.

@lognaturel says that even today on mobile, things don't generally break. Typically the user is looking for something on the lefthand side of the page. However, we think that setting a minimum width would be an improvement.

After we set a minimum width, we will have bounds on the width on both ends: #447 was about setting a maximum width. (The minimum width will likely be set on a different element from the maximum width, but this is just to say that the width of most Frontend content will end up becoming fully bounded.)

[matthew-white]

Right now, there shouldn't ever be a horizontal scrollbar on the page as a whole. However, in #894, I observed that when the entity conflict summary table had a horizontal scrollbar, the page also had a scrollbar. I'm really not sure why that is. I didn't see any overflow from the conflict summary table or the conflict summary box that would cause the page to need a scrollbar. I tried a few things, but I wasn't able to prevent the scrollbar from appearing, so I hid it entirely. However, we will need to show it again once we address this issue. At that time, I think we should take another look at the conflict summary table and try to figure out why there was a scrollbar on the page.