feat(admin): add drag-and-drop group sort order

- Add `sort_order` field to groups table with migration
- Add `PUT /api/v1/admin/groups/sort-order` API for batch update
- Implement drag-and-drop UI using vue-draggable-plus
- All queries now order groups by sort_order
- Add i18n support (en/zh) for sort-related UI text
- Update test stubs to satisfy new interface methods

backend/ent/group/where.go

@@ -165,6 +165,11 @@ func McpXMLInject(v bool) predicate.Group {
 	return predicate.Group(sql.FieldEQ(FieldMcpXMLInject, v))
 }
 
+// SortOrder applies equality check predicate on the "sort_order" field. It's identical to SortOrderEQ.
+func SortOrder(v int) predicate.Group {
+	return predicate.Group(sql.FieldEQ(FieldSortOrder, v))
+}
+
 // CreatedAtEQ applies the EQ predicate on the "created_at" field.
 func CreatedAtEQ(v time.Time) predicate.Group {
 	return predicate.Group(sql.FieldEQ(FieldCreatedAt, v))
@@ -1160,6 +1165,46 @@ func McpXMLInjectNEQ(v bool) predicate.Group {
 	return predicate.Group(sql.FieldNEQ(FieldMcpXMLInject, v))
 }
 
+// SortOrderEQ applies the EQ predicate on the "sort_order" field.
+func SortOrderEQ(v int) predicate.Group {
+	return predicate.Group(sql.FieldEQ(FieldSortOrder, v))
+}
+
+// SortOrderNEQ applies the NEQ predicate on the "sort_order" field.
+func SortOrderNEQ(v int) predicate.Group {
+	return predicate.Group(sql.FieldNEQ(FieldSortOrder, v))
+}
+
+// SortOrderIn applies the In predicate on the "sort_order" field.
+func SortOrderIn(vs ...int) predicate.Group {
+	return predicate.Group(sql.FieldIn(FieldSortOrder, vs...))
+}
+
+// SortOrderNotIn applies the NotIn predicate on the "sort_order" field.
+func SortOrderNotIn(vs ...int) predicate.Group {
+	return predicate.Group(sql.FieldNotIn(FieldSortOrder, vs...))
+}
+
+// SortOrderGT applies the GT predicate on the "sort_order" field.
+func SortOrderGT(v int) predicate.Group {
+	return predicate.Group(sql.FieldGT(FieldSortOrder, v))
+}
+
+// SortOrderGTE applies the GTE predicate on the "sort_order" field.
+func SortOrderGTE(v int) predicate.Group {
+	return predicate.Group(sql.FieldGTE(FieldSortOrder, v))
+}
+
+// SortOrderLT applies the LT predicate on the "sort_order" field.
+func SortOrderLT(v int) predicate.Group {
+	return predicate.Group(sql.FieldLT(FieldSortOrder, v))
+}
+
+// SortOrderLTE applies the LTE predicate on the "sort_order" field.
+func SortOrderLTE(v int) predicate.Group {
+	return predicate.Group(sql.FieldLTE(FieldSortOrder, v))
+}
+
 // HasAPIKeys applies the HasEdge predicate on the "api_keys" edge.
 func HasAPIKeys() predicate.Group {
 	return predicate.Group(func(s *sql.Selector) {