[search] set folder; case insensitive sort (#98335)

* [search] set folder
* sort case insensitive
* fix test

pkg/storage/unified/search/testdata/doc/dashboard-aaa-out.json

@@ -8,7 +8,7 @@
   "kind": "dashboards",
   "rv": 1234,
   "title": "Test title",
-  "title_sort": "Test title",
+  "title_sort": "test title",
   "description": "test description",
   "tags": [
     "a",

pkg/storage/unified/search/testdata/doc/playlist-aaa-out.json

@@ -8,7 +8,7 @@
   "kind": "dashboards",
   "rv": 1234,
   "title": "Test AAA",
-  "title_sort": "Test AAA",
+  "title_sort": "test aaa",
   "created": 1731336353000,
   "createdBy": "user:t000000001",
   "repository": {

pkg/storage/unified/search/testdata/doc/report-aaa-out.json

@@ -8,7 +8,7 @@
   "kind": "dashboards",
   "rv": 1234,
   "title": "Test AAA",
-  "title_sort": "Test AAA",
+  "title_sort": "test aaa",
   "created": 1706690655000,
   "createdBy": "user:abc",
   "repository": {