feat(helpdesk): add handover revision history with timeline, diff, and restore

Every save creates an immutable revision snapshot. The aside shows a
commit-graph-style timeline (newest first) with vertical line, circle
nodes, version numbers, change type, user, and date. Clicking a past
revision renders it readonly with inline git-diff-style highlights
(changed/added/removed with tinted backgrounds). Compare mode allows
diffing any two arbitrary revisions. MANAGE users can restore old
versions, which creates a new revision preserving full history.

New: HandoverRevisionService, HandoverRevisionRepository,
migration 006, 14 PHPUnit tests, DE/EN translations.

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

modules/helpdesk/lib/Module/Helpdesk/Service/HandoverService.php

@@ -45,6 +45,7 @@ class HandoverService
     public function __construct(
         private readonly HandoverRepository $repository,
         private readonly SoftwareProductService $softwareProductService,
+        private readonly ?HandoverRevisionService $revisionService = null,
     ) {
     }
 
@@ -122,6 +123,17 @@ class HandoverService
             return ['ok' => false, 'id' => null, 'errors' => ['general' => t('Failed to create handover')]];
         }
 
+        // Create initial revision (revision 1)
+        $this->revisionService?->createRevision(
+            $tenantId,
+            $id,
+            $fieldValues,
+            self::STATUS_DRAFT,
+            (int) ($schema['version'] ?? 1),
+            $userId,
+            HandoverRevisionService::CHANGE_TYPE_INITIAL
+        );
+
         return ['ok' => true, 'id' => $id, 'errors' => []];
     }
 
@@ -199,6 +211,76 @@ class HandoverService
         return ['ok' => true, 'errors' => []];
     }
 
+    /**
+     * Create a revision snapshot after a combined save (fields + optional status change).
+     * Call this from the action after both updateFields and changeStatus have succeeded.
+     *
+     * @param array<string, mixed> $fieldValues  The final field values
+     */
+    public function createRevisionAfterSave(
+        int $tenantId,
+        int $handoverId,
+        array $fieldValues,
+        string $status,
+        string $previousStatus,
+        int $schemaVersion,
+        int $userId,
+    ): void {
+        if ($this->revisionService === null) {
+            return;
+        }
+
+        $statusChanged = $status !== $previousStatus;
+        $changeType = $statusChanged
+            ? HandoverRevisionService::CHANGE_TYPE_BOTH
+            : HandoverRevisionService::CHANGE_TYPE_FIELDS;
+
+        $this->revisionService->createRevision(
+            $tenantId,
+            $handoverId,
+            $fieldValues,
+            $status,
+            $schemaVersion,
+            $userId,
+            $changeType
+        );
+    }
+
+    /**
+     * Create a revision for a status-only change.
+     */
+    public function createRevisionForStatusChange(
+        int $tenantId,
+        int $handoverId,
+        string $newStatus,
+        int $schemaVersion,
+        int $userId,
+    ): void {
+        if ($this->revisionService === null) {
+            return;
+        }
+
+        $handover = $this->repository->findById($tenantId, $handoverId);
+        if ($handover === null) {
+            return;
+        }
+
+        $fieldValues = json_decode((string) ($handover['field_values'] ?? '{}'), true);
+        if (!is_array($fieldValues)) {
+            $fieldValues = [];
+        }
+
+        $this->revisionService->createRevision(
+            $tenantId,
+            $handoverId,
+            $fieldValues,
+            $newStatus,
+            $schemaVersion,
+            $userId,
+            HandoverRevisionService::CHANGE_TYPE_STATUS
+        );
+    }
+
     /**
      * @return array{total: int, rows: list<array<string, mixed>>}
      */