feat: fire subscription_success telemetry on subscription activation

Wire trackMonthlySubscriptionSucceeded() into both subscription
detection paths so GTM receives a client-side subscription_success
event for ad platform conversion tags (LinkedIn, Meta):

- Legacy flow: SubscriptionRequiredDialogContent watcher
- Workspace flow: billingOperationStore.handleSuccess()

Uses subscription_success (not purchase) to avoid double-counting
with the server-side GA4 Measurement Protocol purchase event and
the existing Google Ads Purchase conversion tag in GTM.

src/platform/cloud/subscription/components/SubscriptionRequiredDialogContent.vue

@@ -236,6 +236,7 @@ watch(
   () => isActiveSubscription.value,
   (isActive) => {
     if (isActive && showCustomPricingTable.value) {
+      telemetry?.trackMonthlySubscriptionSucceeded()
       emit('close', true)
     }
   }

src/platform/workspace/stores/billingOperationStore.test.ts

@@ -47,6 +47,14 @@ vi.mock('@/stores/dialogStore', () => ({
   })
 }))
 
+const mockTrackMonthlySubscriptionSucceeded = vi.fn()
+
+vi.mock('@/platform/telemetry', () => ({
+  useTelemetry: () => ({
+    trackMonthlySubscriptionSucceeded: mockTrackMonthlySubscriptionSucceeded
+  })
+}))
+
 import { workspaceApi } from '@/platform/workspace/api/workspaceApi'
 
 import { useBillingOperationStore } from './billingOperationStore'
@@ -159,6 +167,37 @@ describe('billingOperationStore', () => {
       })
     })
 
+    it('fires purchase telemetry on subscription success', async () => {
+      vi.mocked(workspaceApi.getBillingOpStatus).mockResolvedValue({
+        id: 'op-1',
+        status: 'succeeded',
+        started_at: new Date().toISOString(),
+        completed_at: new Date().toISOString()
+      })
+
+      const store = useBillingOperationStore()
+      store.startOperation('op-1', 'subscription')
+
+      await vi.advanceTimersByTimeAsync(0)
+
+      expect(mockTrackMonthlySubscriptionSucceeded).toHaveBeenCalledOnce()
+    })
+
+    it('does not fire purchase telemetry on topup success', async () => {
+      vi.mocked(workspaceApi.getBillingOpStatus).mockResolvedValue({
+        id: 'op-1',
+        status: 'succeeded',
+        started_at: new Date().toISOString()
+      })
+
+      const store = useBillingOperationStore()
+      store.startOperation('op-1', 'topup')
+
+      await vi.advanceTimersByTimeAsync(0)
+
+      expect(mockTrackMonthlySubscriptionSucceeded).not.toHaveBeenCalled()
+    })
+
     it('shows topup success message for topup operations', async () => {
       vi.mocked(workspaceApi.getBillingOpStatus).mockResolvedValue({
         id: 'op-1',

src/platform/workspace/stores/billingOperationStore.ts

@@ -4,6 +4,7 @@ import { computed, ref } from 'vue'
 
 import { useBillingContext } from '@/composables/billing/useBillingContext'
 import { t } from '@/i18n'
+import { useTelemetry } from '@/platform/telemetry'
 import { useToastStore } from '@/platform/updates/common/toastStore'
 import { workspaceApi } from '@/platform/workspace/api/workspaceApi'
 import { useSettingsDialog } from '@/platform/settings/composables/useSettingsDialog'
@@ -133,6 +134,10 @@ export const useBillingOperationStore = defineStore('billingOperation', () => {
     updateOperationStatus(opId, 'succeeded', null)
     cleanup(opId)
 
+    if (operation.type === 'subscription') {
+      useTelemetry()?.trackMonthlySubscriptionSucceeded()
+    }
+
     const billingContext = useBillingContext()
     await Promise.all([
       billingContext.fetchStatus(),