Document the News layer's own sources, keys and limits

DATA_SOURCES, the README's layer and key tables, CURRENT-STATE and the
changelog describe the News layer as it now is: a configured news server,
or Core's own reading of GDELT (no key), Liveuamap (optional) and World
News API (Local, free plan backlink credited). .env.example gives the
download sizes and the daily read budget; KNOWN-ISSUES lists what machine
coding gets wrong and which disputed areas are named as themselves.

.env.example

@@ -318,7 +318,26 @@ GEMINI_CHAT_MODEL=gemini-3.5-flash-lite
 # Restart after changing. Leave blank for the existing global selection.
 # RADIO_PRIORITY_COUNTRIES=IN,PL
 # Optional: a news server for the News layer (its /api/news/hotspots, /feed
-# and /outline routes), such as https://news.example. The dev server forwards
-# only the layer's own GET requests there, with a 15 s timeout. Unset, Core
-# serves no news and the layer shows itself unavailable. SERVER-SIDE ONLY.
+# and /outline routes), such as https://news.example. The local server
+# forwards only the layer's own GET requests there, with a 15 s timeout. Set,
+# it wins over the settings below. SERVER-SIDE ONLY.
 # GEV_NEWS_ORIGIN=
+#
+# Without a news server Core reads the News layer itself. SERVER-SIDE ONLY.
+# Conflicts need no key: the last 24 h of GDELT events (its 15-minute export
+# files, about 100 KB each, about 10 MB a day; violence only, one report per
+# story at GDELT's place for it), titled from GDELT's GKG files (about 6 MB
+# each, about 23 MB an hour: the newest 3 h are read at start, then each new
+# one). Optional: Liveuamap's mapped reports beside them (paid API,
+# https://liveuamap.com/promo/api), read once every 5 minutes.
+# LIVEUAMAP_API_KEY=
+# Local: the day's news from the outlets of the country in view (free plan
+# of 50 points a day, https://worldnewsapi.com/console/), read once per
+# country every 30 minutes, about 1.5 points a read. Without it Local says
+# "key required". The free plan asks for a visible "World News API" link;
+# the app's Data attribution popover carries it.
+# WORLDNEWSAPI_KEY=
+# The most World News API reads a day (default 30, about 45 points, inside
+# the free plan). After that Local says the daily limit is reached.
+# Raise it on a paid plan.
+# WORLDNEWSAPI_DAILY_READS=30