🎨 Palette: Add visual feedback for disabled buttons

[mapleleaflatte03]

💡 What: Added disabled styling (opacity: 0.5, cursor: not-allowed) for buttons across the app.
🎯 Why: Disabled buttons lacked visual feedback, appearing active and displaying pointer cursors, which could mislead users.
📸 Before/After: Before, disabled buttons looked like active buttons. After, disabled buttons are visually distinct.
♿ Accessibility: Improves visual distinction of interactive states, helping users avoid attempting actions that are currently unavailable.

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PR created automatically by Jules for task 3337063553541040622 started by @mapleleaflatte03

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