🎨 Palette: Add empty state to scanner device list

[CommanderPho]

💡 What: Added a clear empty state message when no devices are found in the Bluetooth scanner list.
🎯 Why: Dynamic lists populated by streams often start empty, leaving the user wondering if the app is working or broken. Providing a clear empty state significantly reduces user confusion.
📸 Before/After: Visual change in the main scanner view.
♿ Accessibility: Provides explicit textual feedback of system state instead of just displaying nothing.

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PR created automatically by Jules for task 12217427679937889409 started by @CommanderPho

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