Address issue where users cannot be assigned to groups in production

Add error handling to the user group assignment to gracefully handle missing `created_at` column in production environments, and document the fix.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: a8a78c07-e900-425c-a577-5b4c5894379d
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/1957c339-2757-4d1f-8e92-e9f71a1ce58e/a8a78c07-e900-425c-a577-5b4c5894379d/yj7Yt4E

server/storage.ts

@@ -689,8 +689,23 @@ export class DatabaseStorage implements IStorage {
   }
 
   async assignUserToGroup(userGroup: InsertUserGroup): Promise<UserGroup> {
-    const [newUserGroup] = await db.insert(userGroups).values(userGroup).returning();
-    return newUserGroup;
+    try {
+      // Try with full schema first (development)
+      const [newUserGroup] = await db.insert(userGroups).values(userGroup).returning();
+      return newUserGroup;
+    } catch (error: any) {
+      // If created_at column doesn't exist (production), insert without it
+      if (error?.code === '42703' && error?.message?.includes('created_at')) {
+        console.log('⚠️ Production mode: user_groups table missing created_at column, inserting without it');
+        const userGroupWithoutCreatedAt = {
+          userId: userGroup.userId,
+          groupId: userGroup.groupId
+        };
+        const [newUserGroup] = await db.insert(userGroups).values(userGroupWithoutCreatedAt).returning();
+        return { ...newUserGroup, createdAt: null };
+      }
+      throw error;
+    }
   }
 
   async removeUserFromGroup(userId: string, groupId: number): Promise<void> {