Purge and check before resuming after a PAUSE

_RESUME_PRINT purges 40 mm with BLOBIFIER_CHECKED (instead of the 2 mm
unretract), so the nozzle is primed, wiped and checked before going back
to the print. A failed purge check raises an error that aborts the whole
resume, AFC_RESUME's restore included, so the printer stays paused; the
next RESUME checks again. RESUME PURGE=0 skips the purge.

The purge check records a failure in _PURGE_CHECK_CFG.last_failed, since
its PAUSE has no effect while the printer is already paused.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -51,6 +51,9 @@ detection, `filament_error_sensitivity`), iHeater chamber heater.
   renames PAUSE/RESUME at startup and wraps them:
   `PAUSE -> AFC_PAUSE -> PAUSE -> PAUSE_BASE`,
   `RESUME -> AFC_RESUME -> RESUME -> HEAT_SOAK_RESUME -> _RESUME_PRINT -> RESUME_BASE`.
+  After a PAUSE, `_RESUME_PRINT` first purges with `BLOBIFIER_CHECKED`
+  (`_RESUME_PURGE`); a failed check raises an error, which aborts the whole
+  chain (AFC_RESUME's restore too), so the printer stays paused.
 - Only one `[save_variables]`, in `macros/save_variables.cfg`.
 - `PRINT_END` and `CANCEL_PRINT` share `_PRINT_CLEANUP` (heaters including
   `iHEATER_OFF`, fan, `M221 S100`, bdwidth off). Anything that must happen