Improve group management by adding parent-child relationships and fixing data validation issues.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 9111ef36-26c8-4085-84ca-a35dc1fec1b5
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/7083d608-d6d3-4a6a-9a27-6286c5109627/1e08dc6e-3788-4c72-923e-ae8af43c2a9a.jpg

shared/schema.ts

@@ -149,7 +149,7 @@ export const groups = pgTable("groups", {
   isActive: boolean("is_active").default(true).notNull(),
   createdAt: timestamp("created_at").defaultNow().notNull(),
   createdBy: uuid("created_by").notNull().references(() => users.id, { onDelete: "set null" }),
-  parentGroupId: uuid("parent_group_id"),
+  parentGroupId: uuid("parent_group_id").references(() => groups.id, { onDelete: "set null" }),
 });
 
 // Group members - can be users, organizations, or other groups