feat: entité CustomerContact pour contacts additionnels d'un client

Entity CustomerContact :
- customer (ManyToOne, CASCADE) : client parent
- firstName, lastName : nom/prénom du contact
- email : adresse email (nullable)
- phone : téléphone (nullable)
- role : fonction dans l'entreprise (Gérant, Comptable, etc.)
- isBillingEmail : si true, reçoit les factures par email
- createdAt / updatedAt : timestamps
- getFullName() : prénom + nom

CustomerContactTest (2 tests, 19 assertions) :
- testConstructor : valeurs par défaut
- testSetters : tous les setters/getters

Migration : CREATE TABLE customer_contact avec FK customer ON DELETE CASCADE

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

migrations/Version20260404091315.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Auto-generated Migration: Please modify to your needs!
+ */
+final class Version20260404091315 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return '';
+    }
+
+    public function up(Schema $schema): void
+    {
+        // this up() migration is auto-generated, please modify it to your needs
+        $this->addSql('CREATE TABLE customer_contact (id INT GENERATED BY DEFAULT AS IDENTITY NOT NULL, first_name VARCHAR(255) NOT NULL, last_name VARCHAR(255) NOT NULL, email VARCHAR(255) DEFAULT NULL, phone VARCHAR(20) DEFAULT NULL, role VARCHAR(100) DEFAULT NULL, is_billing_email BOOLEAN NOT NULL, created_at TIMESTAMP(0) WITHOUT TIME ZONE NOT NULL, updated_at TIMESTAMP(0) WITHOUT TIME ZONE DEFAULT NULL, customer_id INT NOT NULL, PRIMARY KEY (id))');
+        $this->addSql('CREATE INDEX IDX_50BF42869395C3F3 ON customer_contact (customer_id)');
+        $this->addSql('ALTER TABLE customer_contact ADD CONSTRAINT FK_50BF42869395C3F3 FOREIGN KEY (customer_id) REFERENCES customer (id) ON DELETE CASCADE NOT DEFERRABLE');
+    }
+
+    public function down(Schema $schema): void
+    {
+        // this down() migration is auto-generated, please modify it to your needs
+        $this->addSql('ALTER TABLE customer_contact DROP CONSTRAINT FK_50BF42869395C3F3');
+        $this->addSql('DROP TABLE customer_contact');
+    }
+}