watcher: a name removed from the targets leaves the state (closes #223)

At startup, before the first check, Run removes from the loaded state
the domain, hostname and certificate entries of names no longer in
DNSWATCHER_TARGETS, takes those names off each port entry's list of
names and removes a port entry left with none, so the dashboard,
/api/v1/status and the startup notification count only configured
names. A configured domain's own records, saved as a hostname entry
under its name, are kept. Nothing is notified. Each port check, next to
the removal of stale port entries, now also removes the certificate
entries for an address a name no longer resolves to, except while none
of its nameservers answered, as port entries already were.

Model: opus-5-5

TODO.md

@@ -19,6 +19,8 @@ trial run of the finished image: https://git.eeqj.de/sneak/dnswatcher/issues/149
 
 # Completed Steps
 
+- 2026-10-02: a name removed from `DNSWATCHER_TARGETS` leaves the state, and so
+  the dashboard and API, at startup, before the first check (closes #223).
 - 2026-10-02: a record type whose query to a nameserver fails keeps its previous
   records and alerts nothing; the other types are still saved (closes #231).
 - 2026-10-02: a Port Change notification lists the port's domains on a