feat(helpdesk): redesign handover edit page sidebar

- JOIN users table in findById for created/updated-by display names
- Fix row mapping to handle merged JOIN results
- Use product name instead of debitor name in page title
- Sidebar: collapsible customer/product sections, status dropdown,
  audit partial with user attribution

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

modules/helpdesk/lib/Module/Helpdesk/Repository/HandoverRepository.php

@@ -41,7 +41,13 @@ class HandoverRepository
         }
 
         $row = DB::selectOne(
-            'SELECT * FROM helpdesk_handovers WHERE id = ? AND tenant_id = ? LIMIT 1',
+            'SELECT h.*,'
+            . ' uc.display_name AS created_by_label, uc.uuid AS created_by_uuid,'
+            . ' uu.display_name AS updated_by_label, uu.uuid AS updated_by_uuid'
+            . ' FROM helpdesk_handovers h'
+            . ' LEFT JOIN users uc ON uc.id = h.created_by'
+            . ' LEFT JOIN users uu ON uu.id = h.updated_by'
+            . ' WHERE h.id = ? AND h.tenant_id = ? LIMIT 1',
             (string) $id,
             (string) $tenantId
         );
@@ -140,8 +146,18 @@ class HandoverRepository
         if (!is_array($row)) {
             return null;
         }
-        $item = $row['helpdesk_handovers'] ?? $row;
-        if (!is_array($item) || !isset($item['id'])) {
+
+        // JOIN queries return nested arrays keyed by table name — merge all sub-arrays
+        $item = [];
+        foreach ($row as $key => $value) {
+            if (is_array($value)) {
+                $item = array_merge($item, $value);
+            } else {
+                $item[$key] = $value;
+            }
+        }
+
+        if (!isset($item['id'])) {
             return null;
         }