Ensure username is required for new users

Update database schema to make the username field mandatory for all users.

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

init.sql

@@ -31,7 +31,7 @@ CREATE INDEX IDX_session_expire ON sessions(expire);
 -- Création de la table users
 CREATE TABLE users (
   id VARCHAR PRIMARY KEY NOT NULL,
-  username VARCHAR UNIQUE,
+  username VARCHAR UNIQUE NOT NULL,
   email VARCHAR UNIQUE,
   name VARCHAR,
   first_name VARCHAR,

shared/schema.ts

@@ -30,7 +30,7 @@ export const sessions = pgTable(
 // User storage table - supports both Replit Auth and local auth
 export const users = pgTable("users", {
   id: varchar("id").primaryKey().notNull(),
-  username: varchar("username").unique(), // For simple login
+  username: varchar("username").unique().notNull(), // For simple login
   email: varchar("email").unique(),
   name: varchar("name"), // Single name field for compatibility
   firstName: varchar("first_name"),