_build_dns_records() only hardcoded 'api' and 'webui', relying on the
optional service registry for the rest. Built-in services (calendar,
files, mail, webdav) were never registered, so they were absent from
the zone file and tests querying webdav.<domain> via CoreDNS got
NXDOMAIN.
Add _BUILTIN_SERVICE_SUBDOMAINS constant and include those names in
every zone build. Also update _stale and apply_cell_name exclusion
sets so DDNS mode correctly removes them from the parent zone.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
roof
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