Three bugs allowed uploaded gcode files to survive on the printer's SD
card, causing firmware restarts to auto-start old prints hours later.
1. The post-print cleanup retry loop always broke after attempt 1
regardless of delete success — delete_file_async returns False on
failure instead of raising, so the except-based retry never fired.
2. When start_print() failed after uploading, the file was never cleaned
up since on_print_complete never fires for prints that never started.
3. Cleanup failures were logged at DEBUG level, invisible in production.