Add debug subcommand and interactive welcome menu

[sebastianrath]

This PR introduces a new welcome screen with clearer onboarding structure.

Welcome to your Actionforge Runner

📖 Docs: https://docs.actionforge.dev

┃ Choose an option                                                                                                                                                                           
┃ > 🚀 Run a graph — execute a local graph file                                                                                                                                              
┃      actrun <file.act>                                                                                                                                                                     
┃   🔗 Connect to web debug session — paste a session token                                                                                                                                  
┃      actrun debug --session-token <token>                                                                                                                                                  
┃   🤖 Connect as agent — connect to the orchestrator                                                                                                                                        
┃      actrun agent --token <token>