feat(telemetry): track API credit top-up success via audit events (#6500)

Summary
- Add TelemetryEvents.API_CREDIT_TOPUP_SUCCEEDED and provider method
trackApiCreditTopupSucceeded
- Introduce topupTrackerStore to persist pending top-ups per user
(localStorage) and reconcile against recent audit logs
- Hook purchase flow to start tracking before opening Stripe checkout
- Reconcile after fetching audit events (UsageLogsTable) and after
fetchBalance, then emit telemetry, refresh balance, and clear pending
- Minor refactor in customerEventsService to return awaited result

Implementation details
- Matching strategy:
  - Event type: credit_added
  - Time window: createdAt between top-up start time and +24h
  - Amount: if known, e.params.amount must equal expected cents
- Cross-tab/user changes: synchronize via storage event and userId
watcher

Limitations / Follow-up
- Reconciliation fetches only page 1 (limit 10) of events; in
high-volume cases, a recent credit_added could fall outside the first
page
- The window and pagination issue will be "resolved by a followup PR to
core and cloud"

Files touched
- src/stores/topupTrackerStore.ts (new)
- src/components/dialog/content/setting/UsageLogsTable.vue
- src/composables/auth/useFirebaseAuthActions.ts
- src/platform/telemetry/providers/cloud/MixpanelTelemetryProvider.ts
- src/platform/telemetry/types.ts
- src/services/customerEventsService.ts

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6500-feat-telemetry-track-API-credit-top-up-success-via-audit-events-29e6d73d365081169941efae70cf71fe)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Christian Byrne <chrbyrne96@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>

src/composables/auth/useFirebaseAuthActions.ts

@@ -8,6 +8,7 @@ import type { ErrorRecoveryStrategy } from '@/composables/useErrorHandling'
 import { t } from '@/i18n'
 import { isCloud } from '@/platform/distribution/types'
 import { useSubscription } from '@/platform/cloud/subscription/composables/useSubscription'
+import { useTelemetry } from '@/platform/telemetry'
 import { useToastStore } from '@/platform/updates/common/toastStore'
 import { useDialogService } from '@/services/dialogService'
 import { useFirebaseAuthStore } from '@/stores/firebaseAuthStore'
@@ -99,7 +100,7 @@ export const useFirebaseAuthActions = () => {
       )
     }
 
-    // Go to Stripe checkout page
+    useTelemetry()?.startTopupTracking()
     window.open(response.checkout_url, '_blank')
   }, reportError)
 
@@ -116,7 +117,9 @@ export const useFirebaseAuthActions = () => {
   }, reportError)
 
   const fetchBalance = wrapWithErrorHandlingAsync(async () => {
-    return await authStore.fetchBalance()
+    const result = await authStore.fetchBalance()
+    // Top-up completion tracking happens in UsageLogsTable when events are fetched
+    return result
   }, reportError)
 
   const signInWithGoogle = wrapWithErrorHandlingAsync(async () => {