feat: add ON/OFF toggle for host threshold alerts (#1456)

* feat: add ON/OFF toggle for host threshold alerts

Add host_alerts_enabled setting (default ON) as a master switch for CPU,
RAM, and disk host threshold evaluation. When OFF, the four threshold
controls in Settings > Host Alerts are disabled and MonitorService skips
the systeminformation calls and alert dispatch entirely, while clearing
stale suppression state so re-enabling starts fresh.

The dashboard Configuration Status card shows "Off" when host threshold
alerts are disabled. Crash capture, health gate, deploy guardrails,
stack alert rules, and the Docker janitor are all unaffected.

* fix: exit NumberChip edit mode when externally disabled

When the host threshold alerts master toggle is turned OFF while a
NumberChip is in edit mode, force-exit edit mode so the chip renders
the greyed-out button state consistently with the other chips.

frontend/src/components/dashboard/ConfigurationStatus.tsx

@@ -208,7 +208,9 @@ export function ConfigurationStatus({ onOpenSection }: ConfigurationStatusProps
           )}
           <Row
             label="Alert thresholds"
-            value={`CPU ${thresholds.cpuLimit}% · RAM ${thresholds.ramLimit}% · Disk ${thresholds.diskLimit}%`}
+            value={thresholds.hostAlertsEnabled === false
+                ? 'Off'
+                : `CPU ${thresholds.cpuLimit}% · RAM ${thresholds.ramLimit}% · Disk ${thresholds.diskLimit}%`}
             onClick={open('host-alerts')}
           />
           <Row

frontend/src/components/dashboard/__tests__/ConfigurationStatus.test.tsx

@@ -33,7 +33,7 @@ function makePayload(overrides: Partial<ConfigurationStatusPayload> = {}): Confi
       ssoProvider: null,
       scanPolicies: { total: 0, enabled: 0, locked: true },
     },
-    thresholds: { cpuLimit: 90, ramLimit: 90, diskLimit: 90, dockerJanitorGb: 5, globalCrash: false },
+    thresholds: { cpuLimit: 90, ramLimit: 90, diskLimit: 90, dockerJanitorGb: 5, globalCrash: false, hostAlertsEnabled: true },
     backup: { provider: 'disabled', autoUpload: false, locked: false },
     ...overrides,
   };
@@ -118,3 +118,32 @@ describe('ConfigurationStatus row visibility', () => {
     expect(screen.getByText('Google')).toBeDefined();
   });
 });
+
+describe('ConfigurationStatus threshold display', () => {
+  it('renders threshold values when hostAlertsEnabled is true', () => {
+    useConfigurationStatusMock.mockReturnValue({
+      status: makePayload({ thresholds: { cpuLimit: 80, ramLimit: 85, diskLimit: 90, dockerJanitorGb: 5, globalCrash: true, hostAlertsEnabled: true } }),
+      loading: false,
+    });
+    render(<ConfigurationStatus />);
+    expect(screen.getByText('CPU 80% · RAM 85% · Disk 90%')).toBeDefined();
+  });
+
+  it('renders OFF badge when hostAlertsEnabled is false', () => {
+    useConfigurationStatusMock.mockReturnValue({
+      status: makePayload({
+        thresholds: { cpuLimit: 80, ramLimit: 85, diskLimit: 90, dockerJanitorGb: 5, globalCrash: true, hostAlertsEnabled: false },
+      }),
+      loading: false,
+    });
+    render(<ConfigurationStatus />);
+    // StatusBadge uppercases 'Off' to 'OFF'. Since backup.provider is
+    // 'disabled' (also rendered as OFF), there are two OFF badges.
+    // Verify the Alert thresholds row specifically shows OFF.
+    const thresholdRow = screen.getByText('Alert thresholds').closest('button');
+    expect(thresholdRow).toBeDefined();
+    // The OFF badge is the span inside the row that has font-mono + uppercase.
+    const badge = thresholdRow!.querySelector('.font-mono');
+    expect(badge?.textContent?.trim()).toBe('OFF');
+  });
+});

frontend/src/components/dashboard/__tests__/useConfigurationStatus.test.tsx

@@ -51,7 +51,7 @@ beforeEach(() => {
       ssoProvider: null,
       scanPolicies: { total: 0, enabled: 0, locked: true },
     },
-    thresholds: { cpuLimit: 90, ramLimit: 90, diskLimit: 90, dockerJanitorGb: 5, globalCrash: false },
+    thresholds: { cpuLimit: 90, ramLimit: 90, diskLimit: 90, dockerJanitorGb: 5, globalCrash: false, hostAlertsEnabled: true },
     backup: { provider: 'disabled', autoUpload: false, locked: false },
   })));
   useNodesMock.mockReset();

frontend/src/components/dashboard/useConfigurationStatus.ts

@@ -37,6 +37,7 @@ export interface ConfigurationStatus {
     diskLimit: number;
     dockerJanitorGb: number;
     globalCrash: boolean;
+    hostAlertsEnabled: boolean;
   };
   backup: {
     provider: 'disabled' | 'sencho' | 'custom';