Improve CLI error messages with actionable setup guidance (#15)

[bilaldev05]

1-Summary :

This PR improves the developer experience by providing clearer and actionable error messages during CLI setup and server startup.

It addresses Issue #15 by enhancing error handling for common setup failures.

2- Improvements

The following scenarios now provide structured and helpful error messages:

Missing Flutter SDK (Flutter not in PATH)

Unsupported Flutter version

Missing platform tools (Xcode / Android SDK)

Port already in use

Lock file conflict (multiple server instances)

Network socket errors

3- What Was Added :

_printCliError() helper for consistent CLI error formatting

_validateFlutterEnvironment() to check Flutter setup before startup

Improved port binding error handling in startBridgeListener

Better lock file conflict messaging

More actionable troubleshooting guidance in SDK connection errors

4- Example Output
❌ Port 50000 is already in use

Another process is already using this port.

🔧 Suggested Fixes:
• Run: lsof -i :50000
• Kill the process using that port
• flutter-skill --bridge-port=9090
5- Result

Developers now receive clear guidance instead of cryptic failures, reducing confusion during setup.

[charliewwdev]

Thanks for the contribution! A few concerns:

1. Flutter validation is too strict — flutter-skill works without Flutter SDK for CDP/Web/Electron platforms. Requiring Flutter in PATH would break the majority of use cases. The _validateFlutterEnvironment() check should only run when connecting to Flutter apps, not on server startup.

2. Indentation changes — The toJson() reformatting and other whitespace changes make the diff harder to review. Please revert formatting-only changes.

3. exit(1) in library code — Calling exit() directly is an anti-pattern in Dart libraries. Consider throwing exceptions instead and letting the CLI handle them.

4. Good ideas though! — The _printCliError() helper and port-in-use messaging are useful. Could you scope this down to just the error formatting improvements without the Flutter validation?

Happy to merge a focused version!