Issue #3633378: Make the top level items clickable

Issue #3633378

Problem/Motivation

Clicking a top-level administrative navigation item with children currently toggles its submenu instead of navigating directly to the section overview page. This adds unnecessary steps for users familiar with the previous Drupal toolbar.

Proposed resolution

• Make eligible top-level navigation items clickable on desktop.
• Preserve submenu expansion on mobile and touch devices.
• Reuse existing menu destinations rather than hardcoding routes.
• Add a configurable setting, defaulting to enabled.
• Update configuration schema and settings form handling.
• Add Kernel tests for configuration, schema compliance, page attachments, HTML preprocessing, and form submission.
• Preserve compatibility with existing navigation layouts and grouped submenus.

Testing

• JavaScript syntax checks passed locally.
• Git whitespace validation passed locally.
• PHP-based tests and browser-level interactions were not available in the local environment and require CI or manual verification.