The panel was doing the HTTP call itself, which meant any mirror sitting
behind a Cloudflare-style anti-bot check returned "<!doctype html>…" for
a POST from Origin: file:// and JSON.parse choked on it. Moving the
fetch into index.js gets rid of the whole class of browser-context
interceptors (CORS preflights, captive portals, anti-bot pages) and
lets the addon look at the response body before trying to parse it —
an HTML body is now reported cleanly as "server returned an HTML page
instead of JSON".
While there, chain a small mirror list — translate.disroot.org,
translate.plausibility.cloud, lingva.ml — so a single mirror being down
does not take the feature with it. A user whose saved URL points at a
mirror that stopped resolving (translate.argosopentech.com is the
notable case) now transparently gets a translation from the next mirror
in line instead of a stack trace.
Verified end-to-end from Node against both a working URL and a dead
one; the dead one falls through to disroot as expected.
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