Debug Python phases with a debugger

Debugging a failing phase used to mean adding print statements; you can now attach VS Code or any debugpy client and step through your Python phase code with breakpoints.

• Added a debug mode to the CLI (tofupilot run --debug) that starts a debugger listener, runs a single worker, and disables phase timeouts so a breakpoint pause isn't cut off
• Added a Debugging guide covering debug mode and manual debugpy attachment, with a ready-to-use VS Code configuration