Feature implementation from commits 6e856b1..88a5d3c

[codeOwlAI]

PR Summary

Enhance File Operations Handling with Event-based Architecture

Overview

This PR improves file operations handling by introducing an event-based architecture using eventbus and channels, particularly for Android file sharing. It also refactors device unlock handling in QuickToggleService for better security.

Change Types

Type	Description
Enhancement	Added event-based architecture for file operations
Refactor	Improved device unlock handling in QuickToggleService

---

Affected Modules

Module / File	Change Description
src/main/java/com/tailscale/ipn/QuickToggleService.java	Refactored onClick() to use unlockAndRun() for secure device unlock
backend.go	Added eventbus integration, removed directFileRoot parameter, added file operations monitoring
callbacks.go	Added channel variables for ShareFileHelper and SAF paths
fileops.go	Added AndroidFileOps implementation wrapping ShareFileHelper
interfaces.go	Added SetShareFileHelper and SetDirectFileRoot functions
tailscale.go	Added backend restart channel and watchFileOpsChanges goroutine

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Notes for Reviewers

• Verify that the removal of directFileRoot parameter from newBackend() doesn't cause runtime issues
• Confirm that synchronization primitives are correctly implemented to avoid race conditions
• Test the device unlock handling in Android to ensure security is maintained

[codeowlai]

🐛 Correctness Issue

Potential Deadlock in SetDirectFileRoot.

Writing to onFilePath channel without checking if it's full can cause a deadlock if the channel is not being actively read from.

Current Code (Diff):

-	onFilePath <- filePath
+	select {
+	case onFilePath <- filePath:
+	default:
+		// Channel is full, log the issue
+		log.Printf("Unable to set file path: channel full")
+	}

📝 Committable suggestion

‼️ IMPORTANT
Trust, but verify! 🕵️ Please review this suggestion with the care of a code archaeologist - check that it perfectly replaces the highlighted code, preserves all lines, maintains proper indentation, and won't break anything in production. Your future self will thank you! 🚀

Suggested change

	onFilePath <- filePath
	select {
	case onFilePath <- filePath:
	default:
	// Channel is full, log the issue
	log.Printf("Unable to set file path: channel full")
	}