PHLEGM v6 - Automatic machine-crash session capture

When an interactive machine faults during continuous execution, STEP, or RUN, PHLEGMulator now:

1. Stops normal machine execution immediately.
2. Saves a one-off crash snapshot under cfg/sessions/ using:
   <program-or-cart>-<machine>-crash-<Phoenix timestamp>.session.phlegm
3. Saves the crash snapshot directly with SessionSaveSingle(..., activateSession=0), so the active named session and the unnamed backup are not overwritten or refreshed by the crash capture.
4. Closes the crashed interactive session after the best-effort save.

Media naming prefers the inserted cartridge source. For PRG machines it prefers the selected ZIP member and otherwise the last loaded PRG source. Archive/member paths are reduced to a filename stem and invalid Windows filename characters are sanitized.

This behavior is scoped to runtime machine faults (non-empty VM fault state); ordinary HALT/STOP and self-test flows do not create crash sessions.
