feat(helpdesk): add customer engagement analytics page [skip ci]

New "Customer analytics" page under Monitoring: surfaces who is actively in
contact vs. who has gone quiet, so the team can reach out before a customer
slips away.

- KPI tiles: total / active / no-contact / never-in-contact
- "Customers without recent contact" — longest silence first
- "Top customers by communication" — most ticket activity in the period
- Configurable no-contact threshold (helpdesk settings, default 60 days)

CustomerEngagementService aggregates the global ticket snapshot per customer
(same single-pull model as RiskRadarService — no N+1 to BC). Last contact is
the most recent ticket activity; silence beyond the threshold flags the
customer. Revenue ranking deferred (BC OData exposes no per-customer ledger).

All within modules/helpdesk/. Tests + PHPStan green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

modules/helpdesk/tests/Module/Helpdesk/Service/HelpdeskSettingsGatewayTest.php

@@ -78,6 +78,53 @@ class HelpdeskSettingsGatewayTest extends TestCase
         $this->assertNull($gateway->getBasicPassword());
     }
 
+    public function testGetInactivityThresholdDaysDefaultsWhenUnset(): void
+    {
+        $settings = $this->createMock(SettingRepositoryInterface::class);
+        $settings->method('getValue')->willReturn(null);
+
+        $gateway = $this->createGateway($settings);
+        $this->assertSame(
+            HelpdeskSettingsGateway::DEFAULT_INACTIVITY_THRESHOLD_DAYS,
+            $gateway->getInactivityThresholdDays()
+        );
+    }
+
+    public function testGetInactivityThresholdDaysClampsToRange(): void
+    {
+        $settings = $this->createMock(SettingRepositoryInterface::class);
+        $settings->method('getValue')->willReturn('999');
+
+        $gateway = $this->createGateway($settings);
+        // Clamped to the max (365).
+        $this->assertSame(365, $gateway->getInactivityThresholdDays());
+    }
+
+    public function testGetInactivityThresholdDaysFallsBackOnNonNumeric(): void
+    {
+        $settings = $this->createMock(SettingRepositoryInterface::class);
+        $settings->method('getValue')->willReturn('not-a-number');
+
+        $gateway = $this->createGateway($settings);
+        $this->assertSame(
+            HelpdeskSettingsGateway::DEFAULT_INACTIVITY_THRESHOLD_DAYS,
+            $gateway->getInactivityThresholdDays()
+        );
+    }
+
+    public function testSetInactivityThresholdDaysClampsAndPersists(): void
+    {
+        $settings = $this->createMock(SettingRepositoryInterface::class);
+        $settings->expects($this->once())
+            ->method('set')
+            ->with(HelpdeskSettingsGateway::KEY_INACTIVITY_THRESHOLD_DAYS, '7', 'helpdesk.inactivity_threshold_days')
+            ->willReturn(true);
+
+        $gateway = $this->createGateway($settings);
+        // 1 is below the minimum (7) => clamped up.
+        $this->assertTrue($gateway->setInactivityThresholdDays(1));
+    }
+
     public function testSetBasicPasswordEncryptsAndPersists(): void
     {
         $settings = $this->createMock(SettingRepositoryInterface::class);