feat: suppress alerts for unwatched hosts

Hosts with watch: false in config no longer appear in the Alerts page
or nav bar alert counts. Events still appear in the Log of Events.
Hosts without a config entry default to watch: false.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hbd/server/hbdclass.py

@@ -286,7 +286,7 @@ class Host:
             Host.hosts[name] = self
         self.num = num
         self.dyn = False
-        self.watched = True
+        self.watched = False
         self.upcount = 0
         self.interval = 0
         self.doesack = -1