feat(server): support query overcapacity member count of workspace (#12050)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Workspace quota information now includes a new metric: the count of members exceeding seat capacity ("overcapacityMemberCount"), available in both numeric and human-readable formats.
  - The workspace quota display and related queries have been updated to show this new overcapacity member count alongside existing quota metrics.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/models/workspace-user.ts

@@ -289,6 +289,15 @@ export class WorkspaceUserModel extends BaseModel {
     });
   }
 
+  async insufficientSeatMemberCount(workspaceId: string) {
+    return this.db.workspaceUserRole.count({
+      where: {
+        workspaceId,
+        status: WorkspaceMemberStatus.NeedMoreSeat,
+      },
+    });
+  }
+
   async getUserActiveRoles(
     userId: string,
     filter: { role?: WorkspaceRole } = {}