fix(view-mode-switch): drop data-toggle="buttons" to stop Bootstrap null-deref on /search

The search view-mode switch rendered <div class="btn-group" data-toggle="buttons">
with <button routerLink> children and no <input>. On window.load, the bundled
Bootstrap 4 JS runs its load.bs.button.data-api handler, which iterates
[data-toggle="buttons"] .btn and reads .checked on
querySelector('input:not([type="hidden"])'); with no input it dereferences null
and throws an uncaught pageerror ("can't access property 'checked', s is null"),
failing the Playwright consoleErrors test on /search.

The attribute is semantically wrong here (there are no toggle inputs) and inert in
stock ng-bootstrap DSpace; routerLinkActive/[class.active] already drive the active
state, so the list/grid/detail toggle is unchanged visually and functionally.

Fixes dataquest-dev/dspace-customers#931

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Matus Kasak

src/app/shared/view-mode-switch/view-mode-switch.component.html

@@ -1,4 +1,4 @@
-<div class="btn-group" data-toggle="buttons">
+<div class="btn-group">
     <button *ngIf="isToShow(viewModeEnum.ListElement)"
             [attr.aria-current]="currentMode === viewModeEnum.ListElement"
             [attr.aria-label]="'search.view-switch.show-list' | translate"