Fixed collapse arrow disappearing when explanding sections in Mission Start

[kaydikat]

Summary

This PR fixes an issue where the collapse arrow would disappear when expanding a section in Mission Start.

Changes Made

• Ensured the arrow remains visible at all times, consistent with other UI sections.
• Adjusted the visible property in src/sectionHeader.qml.

How to Test

• Expand and collapse sections to verify the arrow remains visible.

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