fix(notifications): neutralize satellite-local node names in alert bodies (#1640)

* fix(notifications): neutralize satellite-local node names in alert bodies

Fleet-aggregated alerts embedded each instance seed name (often Local)
while the hub badge already named the remote. Drop identity prefixes and
use type-aware local wording so attribution stays on the badge.

* fix(docs): correct image-update default check cadence

Operator docs still said six-hour polling; the seeded default is two
hours in interval mode, and the cadence is configurable or cron-based.

* test(notifications): assert hub stamps roster name on neutral remote bodies

Cover the fan-in path that attaches hub roster identity while leaving the
satellite message body unchanged.

backend/src/__tests__/monitor-service.test.ts

@@ -895,7 +895,12 @@ describe('MonitorService - breach state machine', () => {
     const svc = MonitorService.getInstance();
     await (svc as any).evaluate();
 
-    expect(mockDispatchAlert).toHaveBeenCalledWith('warning', 'monitor_alert', expect.stringContaining('CPU'), { stackName: 'my-stack', actor: 'system:monitor' });
+    expect(mockDispatchAlert).toHaveBeenCalledWith(
+      'warning',
+      'monitor_alert',
+      'The **CPU usage** for **my-stack** has exceeded your threshold of **80%** (Currently: 90%).',
+      { stackName: 'my-stack', actor: 'system:monitor' },
+    );
     expect(mockUpdateStackAlertLastFired).toHaveBeenCalledWith(1, expect.any(Number));
   });