Fix mission start arrows

[kaydikat]

Fix Disappearing Collapse Arrow and Align Rotation with UI Standards

Description

This PR fixes an issue where the collapse arrows in the Camera, Vehicle Info, and Launch Postition sections in Mission Start would disappear when expanding sections. Additionally, it updates the arrow behavior to follow standard UI practices, where:

• Collapsed (default) → Arrow points right (-90°).
• Expanded → Arrow points down (0°).

This is consistent with UI/UX conventions in applications like VS Code, where collapse/expand arrows follow the right → down transition.

Before the UI change

After the UI change

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Test Steps

To verify this fix:

1. Open QGroundControl.
2. Click Q in top left corner.
3. Click Plan Flight.
4. Open Mission Start on right side of screen.
5. Click the collapse arrow to the Camera section → Arrow should smoothly rotate right → down.
6. Click again to collapse → Arrow should rotate down → right and remain visible.

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