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/topbar/CurrentUserButton.vue

@@ -45,14 +45,16 @@
           class: 'rounded-lg w-80'
         }
       }"
+      @show="onPopoverShow"
     >
       <!-- Workspace mode: workspace-aware popover (only when ready) -->
       <CurrentUserPopoverWorkspace
         v-if="teamWorkspacesEnabled && initState === 'ready'"
+        ref="workspacePopoverContent"
         @close="closePopover"
       />
       <!-- Legacy mode: original popover -->
-      <CurrentUserPopover
+      <CurrentUserPopoverLegacy
         v-else-if="!teamWorkspacesEnabled"
         @close="closePopover"
       />
@@ -75,7 +77,7 @@ import { isCloud } from '@/platform/distribution/types'
 import { useTeamWorkspaceStore } from '@/platform/workspace/stores/teamWorkspaceStore'
 import { cn } from '@/utils/tailwindUtil'
 
-import CurrentUserPopover from './CurrentUserPopover.vue'
+import CurrentUserPopoverLegacy from './CurrentUserPopoverLegacy.vue'
 
 const CurrentUserPopoverWorkspace = defineAsyncComponent(
   () => import('./CurrentUserPopoverWorkspace.vue')
@@ -112,8 +114,15 @@ const workspaceName = computed(() => {
 })
 
 const popover = ref<InstanceType<typeof Popover> | null>(null)
+const workspacePopoverContent = ref<{
+  refreshBalance: () => void
+} | null>(null)
 
 const closePopover = () => {
   popover.value?.hide()
 }
+
+const onPopoverShow = () => {
+  workspacePopoverContent.value?.refreshBalance()
+}
 </script>