fix(cms): reindex nested array paths correctly in Content Editor

reindexItems replaced the FIRST [n] index in a data-path, which for nested
arrays (e.g. services[1].specs.items) rewrote the OUTER array index instead
of the item's own index. Deleting or adding an item scattered paths across
services[0..n], produced sparse arrays (null items) and schema errors like
'$.details.services[1].specs.items[0]: string érték szükséges'.

Rewrite only the index directly following the reindexed array's path prefix;
drop the now-redundant str-item special case.

Closes MITHOME-30

scripts/test-content-editor-serializer.js

@@ -46,7 +46,7 @@ const document = {
 };
 const browserContext = { document, console, setTimeout, fetch: async () => ({ json: async () => ({ ok: true }) }) };
 vm.createContext(browserContext);
-new vm.Script(`${browserSource}\nglobalThis.__collect = collect;`).runInContext(browserContext);
+new vm.Script(`${browserSource}\nglobalThis.__collect = collect; globalThis.__reindexItems = reindexItems;`).runInContext(browserContext);
 
 assert.deepStrictEqual(JSON.parse(JSON.stringify(browserContext.__collect())), {
   title: 'Módosított',
@@ -54,4 +54,51 @@ assert.deepStrictEqual(JSON.parse(JSON.stringify(browserContext.__collect())), {
   limit: 99,
   sections: [{ id: 'first', items: ['egy', 'kettő'], settings: { visible: false, weight: 3 } }],
 });
+
+// Regression (MITHOME-30): reindexing a NESTED string array (e.g. services[1].specs.items
+// after deleting its first item) must rewrite only the item's own trailing index.
+// The old "replace first [n]" logic rewrote the OUTER array index and scattered the
+// paths across services[0..n], producing sparse arrays and validation errors like
+// "$.details.services[1].specs.items[0]: string érték szükséges".
+const nestedEls = [1, 2, 3, 4, 5, 6].map(n => ({ dataset: { path: `details.services[1].specs.items[${n}]` } }));
+const nestedItems = {
+  dataset: { arrayItems: 'details.services[1].specs.items' },
+  children: nestedEls.map(el => ({
+    querySelectorAll: selector => (selector === '[data-path]' ? [el] : []),
+    querySelector: () => null,
+  })),
+};
+browserContext.__reindexItems(nestedItems);
+assert.deepEqual(nestedEls.map(el => el.dataset.path), [
+  'details.services[1].specs.items[0]',
+  'details.services[1].specs.items[1]',
+  'details.services[1].specs.items[2]',
+  'details.services[1].specs.items[3]',
+  'details.services[1].specs.items[4]',
+  'details.services[1].specs.items[5]',
+]);
+
+// Reindexing the OUTER services array rewrites only the outer index and keeps
+// nested field paths (including nested array item indices) intact.
+const cardEls = [
+  { dataset: { path: 'details.services[2].icon' } },
+  { dataset: { path: 'details.services[2].specs.title' } },
+  { dataset: { path: 'details.services[2].specs.items[4]' } },
+];
+const firstCardEl = { dataset: { path: 'details.services[0].icon' } };
+const servicesItems = {
+  dataset: { arrayItems: 'details.services' },
+  children: [
+    { querySelectorAll: selector => (selector === '[data-path]' ? [firstCardEl] : []), querySelector: () => null },
+    { querySelectorAll: selector => (selector === '[data-path]' ? cardEls : []), querySelector: () => null },
+  ],
+};
+browserContext.__reindexItems(servicesItems);
+assert.equal(firstCardEl.dataset.path, 'details.services[0].icon');
+assert.deepEqual(cardEls.map(el => el.dataset.path), [
+  'details.services[1].icon',
+  'details.services[1].specs.title',
+  'details.services[1].specs.items[4]',
+]);
+
 console.log('Content Editor serializer regression test: OK');