🔒 Fix unhandled unwrap risks in UI button systems

[dynamikdev]

🎯 What: Fixed four instances of a security/stability vulnerability in src/ui/systems.rs where an unhandled unwrap() and risky array indexing (children[0]) could cause the application to panic.

⚠️ Risk: If a button entity is created without children, or if its first child doesn't have a Text component, the children[0] index or the unwrap() call will panic. This could be exploited or accidentally triggered to crash the application, resulting in a Denial of Service (DoS) vulnerability.

🛡️ Solution: Replaced the vulnerable pattern let mut text = text_query.get_mut(children[0]).unwrap(); with idiomatic and safe let-else bindings. The systems now safely attempt to get the first child and its Text component, and gracefully continue the loop if either is missing, preserving application stability.

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PR created automatically by Jules for task 14475550675522544246 started by @dynamikdev

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