test(12.2-05): SPA unit tests for the phase and the check-phase12.2 gate

- sessionKey, dateFormat, FileuploadField (protected thumbnails and
  keyboard reorder backstops), RelationChildModal, RelationPivotModal,
  RelationManager row actions and create-screen deferral, date and time
  list cells; typed deferred relation-schema and file-list fixtures
- scripts/check-phase12.2.sh: go, security (named tests, refuses missing
  or skipped), spa, openapi, dist, docs, hygiene and app stages, a
  detector self-test, one PASS or FAIL line per stage under --all

admin/tests/fixtures/deferred.files.json

@@ -0,0 +1,38 @@
+{
+  "data": [
+    {
+      "id": 41,
+      "file_name": "front.png",
+      "file_size": 120400,
+      "content_type": "image/png",
+      "title": "Front",
+      "description": "",
+      "sort_order": 41,
+      "pending": false,
+      "created_at": "2026-10-02T10:00:00Z"
+    },
+    {
+      "id": 42,
+      "file_name": "back.png",
+      "file_size": 98000,
+      "content_type": "image/png",
+      "title": "",
+      "description": "",
+      "sort_order": 42,
+      "pending": true,
+      "created_at": "2026-10-02T10:05:00Z"
+    },
+    {
+      "id": 43,
+      "file_name": "manual.pdf",
+      "file_size": 2400000,
+      "content_type": "application/pdf",
+      "title": "",
+      "description": "",
+      "sort_order": 43,
+      "pending": false,
+      "created_at": "2026-10-02T10:10:00Z"
+    }
+  ],
+  "meta": {}
+}