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

internal/watcher/export_test.go

@@ -107,6 +107,11 @@ func (w *Watcher) MaybeSendTestNotification(ctx context.Context) {
 	w.maybeSendTestNotification(ctx)
 }
 
+// CleanupRemovedTargets exports cleanupRemovedTargets for testing.
+func (w *Watcher) CleanupRemovedTargets() {
+	w.cleanupRemovedTargets()
+}
+
 // CheckAllPorts exports checkAllPorts for testing.
 func (w *Watcher) CheckAllPorts(ctx context.Context) {
 	w.checkAllPorts(ctx)