feat: Implement client authentication and pre-fill functionality

- Added AuthController for client login and token management.
- Introduced AuthGate for handling authentication state and login UI.
- Updated API to support fetching client data for pre-filling forms.
- Modified App.vue to pre-fill client information if logged in.
- Enhanced client model to include username and password fields.
- Created migration for adding username and password to clients table.
- Added utility for generating secure usernames and passwords.
- Updated frontend to handle client tokens for pre-filling checkout forms.
- Removed old CSS file and updated HTML references to new assets.
- Added StatsOverview widget for displaying client and quote statistics.
- Improved error handling and user feedback in the login process.

backoffice/database/migrations/2026_07_19_100506_add_username_password_to_clienti_table.php

@@ -0,0 +1,30 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('clienti', function (Blueprint $table) {
+            // Nullable: i clienti creati dal checkout pubblico non hanno credenziali di accesso.
+            $table->string('username')->nullable()->unique()->after('id');
+            $table->string('password')->nullable()->after('username');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('clienti', function (Blueprint $table) {
+            $table->dropColumn(['username', 'password']);
+        });
+    }
+};

backoffice/database/migrations/2026_07_19_100618_make_clienti_anagrafica_nullable.php

@@ -0,0 +1,30 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('clienti', function (Blueprint $table) {
+            $table->string('nome')->nullable()->change();
+            $table->string('email')->nullable()->change();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('clienti', function (Blueprint $table) {
+            $table->string('nome')->nullable(false)->change();
+            $table->string('email')->nullable(false)->change();
+        });
+    }
+};