btoa() throws InvalidCharacterError on non-Latin1 input, so feed
names with em-dashes ("The Guardian — World") killed render()
before the dialog's hidden class was removed and nothing visibly
happened on click. Use the loop index for the row id instead.
Visitors can hide individual feeds via a gear-icon panel in the header.
Preferences live in localStorage; the server ships the full source list
(name + channel) as window.PETE_SOURCES so the panel lists every feed,
grouped by channel, regardless of what's on the current page.