docs: re-verify dns-naming.md, no content drift found

Live-checked every specific claim (all 6 per-app zone-presence
examples, forwarders, corrected reverse-zone PTR, DNS-bypass firewall
rule) against Technitium and the firewall directly - all still
accurate. Bumping verified date only.

docs/dns-naming.md

@@ -1,4 +1,4 @@
-<!-- verified: 2026-09-06
+<!-- verified: 2026-09-18
      trilium : nAPJq9A1iuX8, G6NWXtdWX9ap, 0mu75aAXGH8X, fscYadnUtmD5
 -->