fix(ui): set character encoding of html output in blobs
This sets the encoding of the blob made when exporting HTML from the production page to be UTF-8, which prevents weird characters in the output.
(It is worth noting that this HTML is entirely unstyled; it's the raw output from Wax with a very minimal skeleton around it provided by the browser: <html><head></head><body>[WAX CODE]</body></html>
. If this option is to stick around, we could be injecting our CSS into it? Though maybe it's okay to just have raw HTML like this?)