feat: implement discount and transport features in the quote system

- Added maximum discount settings configurable by the administrator.
- Implemented discount calculations in the quote confirmation process.
- Introduced transport options with associated costs, including handling for exceeding maximum piece limits.
- Updated frontend to display discounts and transport information in the quote summary.
- Created new database migrations for storing discount and transport settings.
- Developed a new Filament page for managing global discount settings.
- Enhanced email templates to include discount and transport details.
- Added tests to ensure proper functionality of discounts and transport calculations.

backoffice/app/Models/Impostazione.php

@@ -0,0 +1,52 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Support\Facades\Cache;
+
+class Impostazione extends Model
+{
+    protected $table = 'impostazioni';
+
+    protected $fillable = ['chiave', 'valore'];
+
+    protected $casts = [
+        'valore' => 'json',
+    ];
+
+    private const CACHE_KEY = 'impostazioni';
+
+    /** Valore dell'impostazione, o $default se non è mai stata salvata. */
+    public static function valore(string $chiave, mixed $default = null): mixed
+    {
+        $tutte = Cache::rememberForever(self::CACHE_KEY, fn () => static::query()->pluck('valore', 'chiave')->all());
+
+        return $tutte[$chiave] ?? $default;
+    }
+
+    public static function imposta(string $chiave, mixed $valore): void
+    {
+        static::query()->updateOrCreate(['chiave' => $chiave], ['valore' => $valore]);
+    }
+
+    /**
+     * Regola base di scontistica (%), valida per i clienti senza massimi personalizzati:
+     * quella salvata dall'amministratore, altrimenti config/preventivi.php.
+     *
+     * @return array{max_1:float,max_2:float}
+     */
+    public static function scontiBase(): array
+    {
+        return [
+            'max_1' => (float) static::valore('sconti.max_1', config('preventivi.sconti.max_1')),
+            'max_2' => (float) static::valore('sconti.max_2', config('preventivi.sconti.max_2')),
+        ];
+    }
+
+    protected static function booted(): void
+    {
+        static::saved(fn () => Cache::forget(self::CACHE_KEY));
+        static::deleted(fn () => Cache::forget(self::CACHE_KEY));
+    }
+}