feat(categories) : add bidirectional piece/component category conversion

Backend service and controller for converting piece categories to component
categories (and vice-versa). Uses raw SQL in a transaction to preserve IDs
and transfer all related data (documents, custom fields, constructeurs).
Includes php-cs-fixer formatting pass on existing controllers/entities.

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

src/Enum/ModelCategory.php

@@ -7,6 +7,6 @@ namespace App\Enum;
 enum ModelCategory: string
 {
     case COMPONENT = 'COMPONENT';
-    case PIECE = 'PIECE';
-    case PRODUCT = 'PRODUCT';
+    case PIECE     = 'PIECE';
+    case PRODUCT   = 'PRODUCT';
 }