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/platform/assets/components/UploadModelUpgradeModal.vue

@@ -12,13 +12,13 @@
 </template>
 
 <script setup lang="ts">
+import { useBillingContext } from '@/composables/billing/useBillingContext'
 import UploadModelUpgradeModalBody from '@/platform/assets/components/UploadModelUpgradeModalBody.vue'
 import UploadModelUpgradeModalFooter from '@/platform/assets/components/UploadModelUpgradeModalFooter.vue'
-import { useSubscription } from '@/platform/cloud/subscription/composables/useSubscription'
 import { useDialogStore } from '@/stores/dialogStore'
 
 const dialogStore = useDialogStore()
-const { showSubscriptionDialog } = useSubscription()
+const { showSubscriptionDialog } = useBillingContext()
 
 function handleClose() {
   dialogStore.closeDialog({ key: 'upload-model-upgrade' })