Add setTitle() method to Terminal interface for setting window title. Uses standard OSC escape sequence \x1b]0;...\x07 for broad terminal compatibility (macOS Terminal, iTerm2, Kitty, WezTerm, Ghostty, etc.). Changes: - Add setTitle(title: string) to Terminal interface - Implement in ProcessTerminal using OSC sequence - Implement no-op in VirtualTerminal for testing - Use in interactive mode to set title as "pi - <dirname>"