feat: invite member upsell for single-seat plans (#8801)

## Summary

- Show an upsell dialog when single-seat plan users try to invite
members, with a banner on the members panel directing them to upgrade.
- Misc fixes for member max seat display

## Changes

- **What**: `InviteMemberUpsellDialogContent.vue`,
`MembersPanelContent.vue`, `WorkspacePanelContent.vue`

## Screenshots

<img width="2730" height="1907" alt="image"
src="https://github.com/user-attachments/assets/e39a23be-8533-4ebb-a4ae-2797fc382bc2"
/>
<img width="2730" height="1907" alt="image"
src="https://github.com/user-attachments/assets/bec55867-1088-4d3a-b308-5d5cce64c8ae"
/>



┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8801-feat-invite-member-upsell-for-single-seat-plans-3046d73d365081349b09fe1d4dc572e8)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: GitHub Action <action@github.com>

src/views/GraphView.vue

@@ -16,6 +16,7 @@
   </div>
 
   <GlobalToast />
+  <InviteAcceptedToast />
   <RerouteMigrationToast />
   <ModelImportProgressDialog />
   <ManagerProgressToast />
@@ -44,6 +45,7 @@ import MenuHamburger from '@/components/MenuHamburger.vue'
 import UnloadWindowConfirmDialog from '@/components/dialog/UnloadWindowConfirmDialog.vue'
 import GraphCanvas from '@/components/graph/GraphCanvas.vue'
 import GlobalToast from '@/components/toast/GlobalToast.vue'
+import InviteAcceptedToast from '@/components/toast/InviteAcceptedToast.vue'
 import RerouteMigrationToast from '@/components/toast/RerouteMigrationToast.vue'
 import { useBrowserTabTitle } from '@/composables/useBrowserTabTitle'
 import { useCoreCommands } from '@/composables/useCoreCommands'