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>

README.md

@@ -21,7 +21,7 @@ everything below, grouped by topic. Comment out what you do not use there.
 | `blobifier_hw.cfg` | servo and bucket switch pins | — |
 | **print/** | | |
 | `print_start_end.cfg` | `PRINT_WARMUP`, `PRINT_START`, `PRINT_END` | Beacon, AFC, Blobifier, `HEAT_SOAK`, iHeater, bdwidth, bd_pressure PA macros |
-| `pause_resume.cfg` | `PAUSE`, `RESUME`, `CANCEL_PRINT`, `M600` (RESUME also handles a running `HEAT_SOAK`; CANCEL_PRINT runs the same cleanup as `PRINT_END`) | `heating/heat_soak.cfg`, `leds/` |
+| `pause_resume.cfg` | `PAUSE`, `RESUME`, `CANCEL_PRINT`, `M600` (RESUME also handles a running `HEAT_SOAK`, and after a PAUSE purges 40 mm with `BLOBIFIER_CHECKED` first: a failed check keeps the print paused, `RESUME PURGE=0` skips the purge; CANCEL_PRINT runs the same cleanup as `PRINT_END`) | `heating/heat_soak.cfg`, `leds/`, `blobifier/`, `afc/purge_check.cfg` |
 | `filament.cfg` | `LOAD_FILAMENT`, `UNLOAD_FILAMENT` | — |
 | `homing.cfg` | `HOME` | — |
 | `idle_timeout.cfg` | `[idle_timeout]`: heaters, chamber heater and motors off | iHeater macros |