Add WiFi scan shutdown hook for Android detector

[nbschultz97]

Summary

• add stopScan() to DroneSignalDetector to remove callbacks and unregister the WiFi receiver
• invoke detector.stopScan() from MainActivity.onDestroy
• allow app/ directory to be tracked in git

Testing

• ./gradlew test (fails: No such file or directory)

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https://chatgpt.com/codex/tasks/task_e_68c331b97ea48328ba7bdf51698d89d0

[chatgpt-codex-connector]

Codex Review: Here are some suggestions.

DroneDetectAndroid/app/src/main/java/com/example/dronedetect/DroneSignalDetector.kt

Lines 19 to 22 in 85bfb00

	fun stopScan() {
	handler.removeCallbacksAndMessages(null)
	context.unregisterReceiver(receiver)
	}

[P1] Guard against unregistering unregistered Wi‑Fi receiver

In DroneSignalDetector.stopScan() the code unconditionally calls context.unregisterReceiver(receiver) even though startScan() never registers receiver and MainActivity.onDestroy() invokes stopScan() on every exit. On Android, calling unregisterReceiver for a receiver that was never registered throws IllegalArgumentException, so the app will crash as soon as the activity is destroyed unless scanning was started beforehand. Consider tracking a registration flag or wrapping the unregistration in a try/catch so that destroying the activity without an active scan does not crash the app.

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