test(data-integrity) : add 10 tests for data loss prevention

Tests cover:
- Clone: CustomFieldValue references cloned definitions, not source
- Clone: values are preserved after cloning
- Slots: 404 on non-existent piece, 422 on wrong type, success on correct type
- Conversion: blocked when slots have filled data, allowed when empty
- CustomField: rejects orphan creation, accepts existing field by ID

Also removes legacy JSON structure check (column no longer exists
after normalization) — replaced by slot table checks.

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

src/Service/ModelTypeCategoryConversionService.php

@@ -200,41 +200,6 @@ final class ModelTypeCategoryConversionService
             $blockers[] = sprintf('%d composant(s) lié(s) à des machines.', $machineLinked);
         }
 
-        // Check if any composant has pieces or sub-components in structure
-        $withStructure = $this->connection->fetchAllAssociative(
-            'SELECT name, structure FROM composants WHERE typecomposantid = :id AND structure IS NOT NULL',
-            ['id' => $modelTypeId],
-        );
-
-        foreach ($withStructure as $row) {
-            $structure = json_decode($row['structure'], true);
-
-            if (!is_array($structure)) {
-                continue;
-            }
-
-            $hasPieces        = !empty($structure['pieces']);
-            $hasSubcomponents = !empty($structure['subcomponents']);
-
-            if ($hasPieces || $hasSubcomponents) {
-                $parts = [];
-
-                if ($hasPieces) {
-                    $parts[] = 'pièces';
-                }
-
-                if ($hasSubcomponents) {
-                    $parts[] = 'sous-composants';
-                }
-
-                $blockers[] = sprintf(
-                    'Le composant « %s » contient des %s dans sa structure.',
-                    $row['name'],
-                    implode(' et ', $parts),
-                );
-            }
-        }
-
         // Check slot tables for actual data (post-normalization architecture)
         $filledPieceSlots = (int) $this->connection->fetchOne(
             'SELECT COUNT(*) FROM composant_piece_slots cps