fix(news): answer within the browser's wait on a first read

A country's first World News API read, or Liveuamap's, could take up to
20 s while the browser waits 15, so the panel showed the browser's own
"signal timed out". A read with nothing to serve yet is now waited for
at most 12 s, as GDELT's already was: past that the section answers
unavailable while the read goes on, and the next refresh is served from
it. A client timeout reads "News feed unavailable".

docs/KNOWN-ISSUES.md

@@ -145,6 +145,9 @@ Status: Open (limits)
 - A country's own stories in Local keep World News API's category (politics as
   political, business as economy, else other) and carry no severity; fighting
   there shows through the Conflicts reports placed in the area.
+- When World News API takes over 12 s to answer a country's first read, Local
+  reads unavailable until the layer's next refresh (up to 2 minutes), which is
+  served from that read.
 - Local needs a World News API key. Its free plan allows 50 points a day; Core
   stops at `WORLDNEWSAPI_DAILY_READS` reads (default 30) and Local then says the
   daily limit is reached.