feat(machine) : single save button + link versioning with restore

Backend:
- Enrich machine snapshot with componentLinks/pieceLinks/productLinks
- Detect link add/remove in MachineAuditSubscriber onFlush
- Add link diff comparison in restore preview
- Add link restoration in applyRestore for machines
- Add integrity warnings for missing linked entities

Frontend (submodule update):
- Single save button replacing auto-save-on-blur
- Link versioning display in version list and restore modal

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

migrations/Version20260326120000.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260326120000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Add referenceFormula and requiredFieldsForReference to model_types, referenceAuto to pieces';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE model_types ADD COLUMN IF NOT EXISTS referenceformula TEXT DEFAULT NULL');
+        $this->addSql('ALTER TABLE model_types ADD COLUMN IF NOT EXISTS requiredfieldsforreference JSON DEFAULT NULL');
+        $this->addSql('ALTER TABLE pieces ADD COLUMN IF NOT EXISTS referenceauto VARCHAR(255) DEFAULT NULL');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE pieces DROP COLUMN IF EXISTS referenceauto');
+        $this->addSql('ALTER TABLE model_types DROP COLUMN IF EXISTS requiredfieldsforreference');
+        $this->addSql('ALTER TABLE model_types DROP COLUMN IF EXISTS referenceformula');
+    }
+}