ADFA-5184 fix(web): correct the "server not responding" banner copy

[luisguzman-adfa]

Fixes the served landing page's "backend not responding" banner, which gave
wrong and outdated guidance, per ADFA-5184.

The banner told the user to open Termux and run iiab-termux --start. That's
wrong on two counts: it assumes the only cause is a stopped server (the server
may simply be starting up, or its hotspot/address changed), and Termux was
dropped two iterations ago, so the command no longer applies. It's also aimed at
the host, but the banner is what a guest sees.

What changes (copy only, no logic):

• Rewrote the backend_error string: neutral wording that doesn't assume a single
  cause, states the page reconnects on its own (the JS already polls every 5–60 s
  and self-heals), and points to rescanning the code if the address changed.
• Removed the iiab-termux --start line from index.html.
• Updated the English default and all 32 other locale files.

New copy:
"The K2Go server isn't responding. Make sure K2Go is running on the host
device; the page reconnects on its own. If it doesn't come back, rescan the
code to get its current address."

Scope: static/site only (index.html + lang/*.js). No app/native change.

l10n: default + 32 locales. Locale strings are machine-translated, pending native
review for bn/gu/ta/sw/az/yo/sr.

Verification: node --check passes on all 33 lang files; no "termux" reference
remains under static/site. Renders on-device after a rootfs rebuild (the served
site ships in the rootfs).