Fix user creation errors by handling empty emails properly

Adjust user creation schema to allow null emails, update data handling to convert empty strings to null, and provide a SQL script to clean up existing duplicate empty email entries, resolving the `users_email_key` constraint violation.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: a8a78c07-e900-425c-a577-5b4c5894379d
Replit-Commit-Checkpoint-Type: full_checkpoint
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server/routes.ts

@@ -921,7 +921,7 @@ export async function registerRoutes(app: Express): Promise<Server> {
       const createUserSchema = z.object({
         id: z.string().optional(),
         username: z.string().min(1, "L'identifiant est obligatoire"),
-        email: z.union([z.string().email(), z.literal("")]).optional(),
+        email: z.union([z.string().email(), z.literal(""), z.null()]).optional(),
         firstName: z.string().optional(),
         lastName: z.string().optional(),
         password: z.string().min(1, "Le mot de passe est obligatoire"),
@@ -952,7 +952,7 @@ export async function registerRoutes(app: Express): Promise<Server> {
       const userToCreate = {
         id: newUserId,
         username: userData.username,
-        email: userData.email || '',
+        email: userData.email && userData.email.trim() !== '' ? userData.email : null, // Use NULL instead of empty string
         firstName: userData.firstName || '',
         lastName: userData.lastName || '',
         password: hashedPassword,