fix(xtream): scope category bulk actions to search results (#1534)

.changes/xtream-filtered-category-selection.md

@@ -0,0 +1,7 @@
+---
+type: fix
+area: xtream
+issues: [812, 816]
+---
+
+Xtream category management now selects or deselects only matching categories while searching, preserving the visibility of all other categories. Button labels and availability reflect the search results, and the counter clearly shows the total selected.