feat: multiline loop parsing and hidden autostart improvement

[bosiakov]

• Parse multiline loops (for/while/until/select/do-while) across bash, zsh, and powershell
• Treat loop constructs as single tokens in the prefix tree (same as function definitions)
• Merge leading env var assignments (KEY=VALUE) with the command name into a single tree node
• Add --hidden CLI flag; autostart registrations (LaunchAgent, registry, .desktop) pass it so the app starts in the tray on boot but shows the window on manual launch
• Remove StartHidden config field and configExisted bool from LoadConfig