feat: fire subscription_success telemetry on subscription activation (#10186)

## Summary

Fire a client-side `subscription_success` event to GTM when a
subscription activates, enabling LinkedIn and Meta conversion tracking
tags.

## Changes

- **What**: Wire `trackMonthlySubscriptionSucceeded()` into both
subscription detection paths (legacy dialog watcher + workspace
billingOperationStore). This method existed but had zero call sites
(dead code). The event name remains `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.

## Review Focus

- billingOperationStore only fires telemetry for `subscription`
operations, not `topup`.
- Legacy flow: telemetry fires in the existing `isActiveSubscription`
watcher, before `emit("close", true)`.
- Workspace flow: telemetry fires in `handleSuccess()` after status
update but before billing context refresh.
- No event name change: `subscription_success` was the original name and
avoids collision with the server-side `purchase` event.

---------

Co-authored-by: Benjamin Lu <benjaminlu1107@gmail.com>

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/telemetry/providers/cloud/GtmTelemetryProvider.test.ts

@@ -90,6 +90,14 @@ describe('GtmTelemetryProvider', () => {
       expect(lastDataLayerEntry()).toMatchObject({ event: 'select_promotion' })
     })
 
+    it('pushes subscription_success for subscription activation', () => {
+      const provider = createInitializedProvider()
+      provider.trackMonthlySubscriptionSucceeded()
+      expect(lastDataLayerEntry()).toMatchObject({
+        event: 'subscription_success'
+      })
+    })
+
     it('pushes run_workflow with trigger_source', () => {
       const provider = createInitializedProvider()
       provider.trackRunButton({ trigger_source: 'button' })

src/platform/telemetry/providers/cloud/GtmTelemetryProvider.ts

@@ -165,6 +165,10 @@ export class GtmTelemetryProvider implements TelemetryProvider {
     this.pushEvent('signup_opened')
   }
 
+  trackMonthlySubscriptionSucceeded(): void {
+    this.pushEvent('subscription_success')
+  }
+
   trackRunButton(options?: {
     subscribe_to_run?: boolean
     trigger_source?: ExecutionTriggerSource

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(),