🔒 Fix potential panic on UI button interaction

[dynamikdev]

🎯 What: Fixed a security vulnerability in UI button interaction systems where unwrap() and direct index access (children[0]) were used.\n⚠️ Risk: Potential panic/Denial of Service (DoS). If the button had no children or if the child was not a Text component, the application would crash.\n🛡️ Solution: Replaced let mut text = text_query.get_mut(children[0]).unwrap(); with safe access patterns using let-else:\n rust\n let Some(&child) = children.first() else { continue; };\n let Ok(mut text) = text_query.get_mut(child) else { continue; };\n \nThis was proactively applied to sequence_control_button_system, curriculum_toggle_system, mode_toggle_system, and rhythm_mode_toggle_system.

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PR created automatically by Jules for task 9738410101036695000 started by @dynamikdev

[google-labs-jules]

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