🧹 Extract error cleanup interval constant in main.rs

[myaple]

🎯 What:
Replaced the magic number 30 in src/main.rs with a named constant ERROR_CLEANUP_INTERVAL_SECS.

💡 Why:
Using a named constant improves code readability and maintainability by making the purpose of the value clear and easier to modify in the future.

✅ Verification:

• Ran cargo test to ensure no regressions.
• Verified that the logic remains unchanged, only the representation of the value.

✨ Result:
The error cleanup interval is now defined as a constant at the top of the file.

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PR created automatically by Jules for task 9100651059346629862 started by @myaple

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