content,dns: resolve proxy fake IP addresses safely

Use DNS over HTTPS only when a host has only proxy fake IP addresses.
Keep private address checks and pinned article connections.
Test DNS failures, redirects, and interruption.

.env.example

@@ -24,3 +24,7 @@ AI_MODELS='[{"id":"gemini-flash","name":"Gemini Flash","provider":"google","mode
 # Set the RSS worker limits.
 RSS_POLL_SECONDS=900
 RSS_CONCURRENCY=2
+
+# Set the DNS over HTTPS fallback for proxy fake IP addresses.
+# Set this value to off to disable the fallback.
+DNS_OVER_HTTPS_URL=https://cloudflare-dns.com/dns-query