Fix nav bar CollapseButton behavior

[phil-snowplow]

Fixes https://snplow.atlassian.net/browse/DOC-122.

• Problem: The expand/collapse arrow was both expanding the sidebar
  section AND navigating to the category page
• Root cause: The CollapseButton component was
  programmatically clicking the link element after expanding
• Solution: Simplified the handleClick function to only toggle the
  collapse state (updateCollapsed(!collapsed)) without any navigation logic

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