🎨 Palette: [UX improvement] Fix mnemonic clash & add a11y names to error popups

[awest813]

💡 What:

• Changed the speedSliderLabel mnemonic in AnimationControllerPanel from Alt+S to Alt+E.
• Added pane.getAccessibleContext().setAccessibleName("Error details stack trace") to the JTextPane objects in ExceptionPopup.java.

🎯 Why:

• The speed slider label previously conflicted with the animationBoxLabel which also used Alt+S. Changing it to E makes the keyboard shortcut functional without conflict.
• The JTextPane objects in the error popups were not readable by screen readers. Adding an accessible name allows screen readers to provide proper context to the user regarding the contents of the read-only area.

♿ Accessibility:

• Improves screen reader context and keyboard navigation reliability in desktop UI components.

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PR created automatically by Jules for task 9404533160152970540 started by @awest813

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