feat(piece) : add quantity field to MachinePieceLink entity + migration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

migrations/Version20260309150000.php

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260309150000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Add quantity column to machine_piece_links table';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE machine_piece_links ADD COLUMN IF NOT EXISTS quantity INTEGER NOT NULL DEFAULT 1');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE machine_piece_links DROP COLUMN IF EXISTS quantity');
+    }
+}