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__/docker-event-service.test.ts

@@ -137,7 +137,7 @@ describe('DockerEventService - die classification', () => {
         expect(mockDispatchAlert).toHaveBeenCalledWith(
             'error',
             'monitor_alert',
-            expect.stringContaining('Container Crash Detected'),
+            'Container Crash Detected: web exited unexpectedly (Code: 1).',
             expect.objectContaining({ containerName: 'web' }),
         );
     });
@@ -588,8 +588,8 @@ describe('DockerEventService - reconnect', () => {
 
         const warn = mockDispatchAlert.mock.calls.find(c => c[0] === 'warning');
         const info = mockDispatchAlert.mock.calls.find(c => c[0] === 'info');
-        expect(warn?.[2]).toContain('Lost connection');
-        expect(info?.[2]).toContain('Reconnected');
+        expect(warn?.[2]).toBe('Lost connection to Docker daemon; monitoring paused.');
+        expect(info?.[2]).toBe('Reconnected to Docker daemon.');
     });
 
     it('shutdown cancels pending reconnect', async () => {