feat: host-level watch flag suppresses notifications; filter dashboard/overview by owner/manager; add ZFS monitor plugin

- watch: true (default) per host; watch: false suppresses all notifications
  for that host in udp.py and threshold.py
- Live Dashboard and Host Overview now show only hosts where the logged-in
  user is owner or manager (admins see all); WebSocket broadcasts filtered
  per-connection by the same rule
- Add hbd/client/plugins/zfs_monitor.py: collects per-pool health, capacity,
  fragmentation, dedup ratio, and cumulative I/O ops/bandwidth via zpool(8)

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

hbd/server/threshold.py

@@ -9,6 +9,7 @@ This module provides a flexible threshold checking system that:
 - Supports multiple comparison operators
 """
 
+import asyncio
 import logging
 import time
 from enum import Enum
@@ -1020,6 +1021,11 @@ class ThresholdChecker:
         value: Any,
     ):
         """Send notification and log to journal/eventlog."""
+        from . import hbdclass
+        host = hbdclass.Host.hosts.get(host_name)
+        if host is not None and not host.watched:
+            eventlog(host_name, lvl, message, service="threshold")
+            return
         asyncio.get_event_loop().create_task(notify_mod.send_notification(
             host_name,
             notify_mod.Notification(
@@ -1032,7 +1038,6 @@ class ThresholdChecker:
         # Log to journal
         if self.journal is not None:
             try:
-                import asyncio
                 loop = asyncio.get_event_loop()
                 loop.create_task(self.journal.log_threshold_event(
                     host_name=host_name,
@@ -1224,17 +1229,20 @@ class ThresholdChecker:
             else:
                 message = f"REMINDER ({alert_state.level.name}): {host_name} - {metric_path} = {value} (ongoing for {int(now - alert_state.since)}s)"
             
-            asyncio.get_event_loop().create_task(notify_mod.send_notification(
-                host_name,
-                notify_mod.Notification(
-                    title=f"[REMINDER/{alert_state.level.name}] {host_name}",
-                    body=message,
-                    level=alert_state.level.name,
-                ),
-            ))
+            from . import hbdclass
+            host = hbdclass.Host.hosts.get(host_name)
+            if host is None or host.watched:
+                asyncio.get_event_loop().create_task(notify_mod.send_notification(
+                    host_name,
+                    notify_mod.Notification(
+                        title=f"[REMINDER/{alert_state.level.name}] {host_name}",
+                        body=message,
+                        level=alert_state.level.name,
+                    ),
+                ))
+                logger.info("Re-notification sent: %s", message)
             alert_state.last_notification = now
             alert_state.notification_count += 1
-            logger.info("Re-notification sent: %s", message)
     
     def get_active_alerts(self, alert_states: Dict[str, AlertState]) -> list:
         """