Feat/workspaces 6 billing (#8508)

## Summary

Implements billing infrastructure for team workspaces, separate from
legacy personal billing.

## Changes

- **Billing abstraction**: New `useBillingContext` composable that
switches between legacy (personal) and workspace billing based on
context
- **Workspace subscription flows**: Pricing tables, plan transitions,
cancellation dialogs, and payment preview components for workspace
billing
- **Top-up credits**: Workspace-specific top-up dialog with polling for
payment confirmation
- **Workspace API**: Extended with billing endpoints (subscriptions,
invoices, payment methods, credits top-up)
- **Workspace switcher**: Now displays tier badges for each workspace
- **Subscribe polling**: Added polling mechanisms
(`useSubscribePolling`, `useTopupPolling`) for async payment flows

## Review Focus

- Billing flow correctness for workspace vs legacy contexts
- Polling timeout and error handling in payment flows

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8508-Feat-workspaces-6-billing-2f96d73d365081f69f65c1ddf369010d)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

src/composables/auth/useFirebaseAuthActions.ts

@@ -2,11 +2,11 @@ import { FirebaseError } from 'firebase/app'
 import { AuthErrorCodes } from 'firebase/auth'
 import { ref } from 'vue'
 
+import { useBillingContext } from '@/composables/billing/useBillingContext'
 import { useErrorHandling } from '@/composables/useErrorHandling'
 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'
@@ -83,7 +83,7 @@ export const useFirebaseAuthActions = () => {
   )
 
   const purchaseCredits = wrapWithErrorHandlingAsync(async (amount: number) => {
-    const { isActiveSubscription } = useSubscription()
+    const { isActiveSubscription } = useBillingContext()
     if (!isActiveSubscription.value) return
 
     const response = await authStore.initiateCreditPurchase({