Doctor now checks configErr and emits a FAIL with the parse error and
fix hint. Execute() no longer prints a separate error before running
doctor — the doctor output is self-contained.
Only config edit, config init, config path, and doctor run with a
broken config. Destructive commands like config set (which would
overwrite a partially-valid file with defaults) are now blocked.
Suppresses the warning on safe commands. Adds "Running pda! doctor"
header before diagnostic output.
When the config file is malformed, config and doctor commands now
proceed with defaults (showing a warning). All other commands print
the parse error and automatically run doctor to aid diagnosis.
