Correct page a11y issues

[jlandiseigsti]

Our accessibility site should be the beacon of web accessibility, right?

Address issues found by checkers. There aren't very many but:

• Uppy forms show up as having missing form labels
• Uppy forms have some low color-contrast text
• Site language not declared

[jlandiseigsti]

The Uppy widget has two hidden inputs without labels, which the autochecker hates. However, they are marked as aria-ignore, so they will not confuse any screen reader users. Given that it is not our widget and digging into the specifics of how its form is rendered would be complex, I think we should mark this as "Won't Do."