Allow clearing user name and email fields through the interface

Update frontend and backend to permit empty strings for firstName, lastName, and email fields when updating user data, addressing an issue where clearing these fields was not persisted.

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/vetH0Gp

server/routes.ts

@@ -935,8 +935,8 @@ export async function registerRoutes(app: Express): Promise<Server> {
       const updateUserSchema = z.object({
         username: z.string().optional(),
         role: z.enum(['admin', 'manager', 'employee']).optional(),
-        firstName: z.string().optional(),
-        lastName: z.string().optional(),
+        firstName: z.union([z.string(), z.literal("")]).optional(),
+        lastName: z.union([z.string(), z.literal("")]).optional(),
         email: z.union([z.string().email(), z.literal("")]).optional(),
         password: z.string().optional(),
       });