🎨 Palette: Improve accessibility of node_modules collapsible section

[acebytes]

💡 What: Added explicit accessibility traits and values to the "Project node_modules" collapsible header button.
🎯 Why: Custom buttons that function as disclosure groups need explicit state descriptions so VoiceOver users know if the section is currently expanded or collapsed.
📸 Before/After: Visuals are identical, but VoiceOver now correctly announces the section's state.
♿ Accessibility: Added .accessibilityElement(children: .combine), .accessibilityAddTraits(.isButton), .accessibilityValue, and .accessibilityHint to enhance the screen reader experience.

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PR created automatically by Jules for task 1964374828933525193 started by @acebytes

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