Mark signed zones with a padlock, and name clients in statistics

The zones list shows a padlock after signed zones, linking to their
DNSSEC tab. Client lists in the statistics show the host name Jarl's
records have for each address (PTR, else A/AAAA); no DNS queries.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/stats.md

@@ -111,6 +111,16 @@ Nothing else is stored. In particular there's no per-query record, so you
 can't look up "who asked for X at 14:02". That is deliberate, both for size
 and privacy.
 
+**Client names.** Where the client lists (busiest and refused clients) show
+an address Jarl has a record for, they show its host name too: the PTR
+record's target, or else the name of an A/AAAA record with that address
+(disabled records don't count, and only records you may read). This is
+looked up in Jarl's own data when the list is shown, not stored and not
+asked of DNS, so it is instant and adds no queries of its own. The name is
+what the records say now: with DHCP, an address seen last week may have
+been another machine. Anonymized clients (`anonymize_clients`) are
+prefixes and get no name.
+
 ## Using it
 
 **Web UI**: Statistics. Pick a range (1 hour to 90 days); everything on the