🎨 Palette: Improve empty state in Unresolved Files

[jspann21]

💡 What: Added a helpful suggestion ("If you expected files here, you can add more library folders in Settings.") to the empty state in the Unresolved Files section.
🎯 Why: Previously, the empty state ("No unresolved files — great job! 🎉") acted as a dead-end for users who might actually be expecting files to appear. Giving them an actionable next step makes the UI more helpful and intuitive.
📸 Before/After: Added the screenshot in the verification. Visually, the empty state text is centered nicely with a lighter subtitle.
♿ Accessibility: The new message helps guide users logically on what their next potential action could be if the state isn't what they expect.

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PR created automatically by Jules for task 8229245937247071930 started by @jspann21

[google-labs-jules]

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