🐛 Bug: Sidebar sub-navigation does not auto-collapse

Describe the bug

The documentation sidebar allows multiple sub-navigation sections to remain expanded at the same time. When a new section is opened, the previously expanded section stays open.

This results in a cluttered sidebar and makes navigation harder, especially as more sections are expanded.

This behavior differs from the commonly expected accordion-style navigation used in documentation sidebars, where only one section is expanded at a time.

Steps To Reproduce

1. Open any documentation page.
2. Expand a sidebar section (e.g. Get Started).
3. Expand another sidebar section (e.g. Guides).
4. Observe that the previously expanded section remains open.

Expected Behavior

When a sidebar sub-navigation section is expanded, any previously expanded section should automatically collapse.
Only one sidebar section should be expanded at a time.

Actual Behaviour

Multiple sidebar sections can remain expanded simultaneously.

Why this matters

• Reduces visual clutter in the sidebar
• Improves scanability and navigation speed
• Aligns with common accordion navigation patterns used in docs sites
• Simplifies focus for keyboard and screen reader users

Screenshots/Clips

https://github.com/user-attachments/assets/2bfed81c-8262-40be-be1b-5e797eec152e

Device Information [optional]

- **OS:** macOS  
- **Browser:** Firefox/Chrome

Additional Notes

This appears to be a UI state-management issue where expanded sections are handled independently rather than as a single active section.

Are you working on this issue?

Yes

Do you think this work might require an [Architectural Decision Record (ADR)]? (significant or noteworthy)

No

Start by reproducing the sidebar behavior on a documentation page: expand Get Started, then Guides, and confirm both remain open. Trace the sidebar's expanded-section state management, then verify that opening one section collapses the previously expanded section and that only one section remains open.