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/udp.py

@@ -333,6 +333,8 @@ def handle_datagram(msg: dict, addr, transport, ctx: dict):
         # Use new config function to check dyndns
         dyndnshosts = config_mod.get_dyndnshosts(cfg)
         host.dyn = uname in dyndnshosts
+        watchhosts = config_mod.get_watchhosts(cfg)
+        host.watched = uname in watchhosts
         # Apply user-access settings from config
         access = config_mod.get_host_access(cfg, uname)
         host.apply_access(access["owner"], access["managers"], access["monitors"])