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/components/dialog/header/SettingDialogHeader.vue

@@ -1,6 +1,6 @@
 <template>
   <div>
-    <h2 class="px-4">
+    <h2 :class="cn(flags.teamWorkspacesEnabled ? 'px-6' : 'px-4')">
       <i class="pi pi-cog" />
       <span>{{ $t('g.settings') }}</span>
       <Tag
@@ -16,6 +16,9 @@
 import Tag from 'primevue/tag'
 
 import { isStaging } from '@/config/staging'
+import { useFeatureFlags } from '@/composables/useFeatureFlags'
+import { cn } from '@comfyorg/tailwind-utils'
+const { flags } = useFeatureFlags()
 </script>
 
 <style scoped>