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.

turbo.json

@@ -34,6 +34,7 @@
     "ANTHROPIC_API_KEY",
     "RSS_POLL_SECONDS",
     "RSS_CONCURRENCY",
+    "DNS_OVER_HTTPS_URL",
     "TEST_APP_ORIGIN",
     "TEST_BASE_URL",
     "TEST_ADMIN_PASSWORD",