Add degoog as the search provider, and make it the default

The operator already runs it, so this is the one provider that costs nothing to adopt: no key,
no card, no third party, and no new container. It aggregates several engines and returns them
merged, and its /api/search reply is already the shape everything downstream expects — title,
url, snippet, with content as a fallback for the roughly one result in six that has no snippet.

It is also now the only provider whose response has been read from a live service rather than
from documentation, which is why it is the default.

Deployment/master.conf.template

@@ -1837,13 +1837,15 @@
 # when it is ticked. A question about this machine hands off to the assistant before the search
 # would run, so it never reaches the internet even with the box ticked.
 #
-# Provider: searxng | brave | tavily
+# Provider: degoog | searxng | brave | tavily
+#   degoog   self-hosted, no key — set HOST*_DEGOOG_URL. Aggregates several engines and returns
+#            them merged. The default, and the only one verified against a live service here
 #   searxng  self-hosted, no key, no third party — set HOST*_SEARXNG_URL, and enable format: [json]
 #            in its own settings.yml, which the default image ships with off
 #   brave    HOST*_WEB_SEARCH_API_KEY, free tier available
 #   tavily   HOST*_WEB_SEARCH_API_KEY
     AI_WEB_SEARCH_ENABLED=false
-    AI_WEB_SEARCH_PROVIDER=searxng
+    AI_WEB_SEARCH_PROVIDER=degoog
     AI_WEB_SEARCH_RESULTS=4
     AI_WEB_SEARCH_TIMEOUT=6