cooling_filter_enabled existed as a config option but was shown nowhere,
and there was no capability flag to gate it. The cooling filter and air
filtration are alternative accessories sharing the same duct, so a
printer declares one or the other.
- new hidden printer capability flag support_cooling_filter
- "Use cooling filter" toggle in the Accessory group, shown only when
the printer supports it; the air-filtration toggle hides in that case
(no vendor restriction: third-party printers keep air filtration)
- explicit defaults (0) in the common machine base
- H2C declares support_cooling_filter=1 instead of support_air_filtration;
its start-gcode already carries the cooling-filter conditional, so the
toggle is functional. On H2C this drops the two exhaust-fan lines that
air filtration emitted for ABS-class filaments, matching the printer's
actual duct accessory; H2C is new on this branch so no existing user
output changes.
Printers without the flag keep exactly the previous accessory UI and
g-code.