Print commands carry the external spool as -1 in the flat ams_mapping
(the firmware rejects 254/255 there) and the real target only in
ams_mapping2. We captured only the flat list, so external-spool prints
looked unmapped and the usage tracker's position-based fallback
charged them to the first loaded AMS tray.
- Resolve external spools from ams_mapping2 when capturing a
project_file (dual-nozzle keeps 254/255, single-nozzle -> 254)
- Tracker: an explicit -1 no longer falls back to a positional tray;
a mapping naming no tray for any used slot defers to tray_now
- Keep the #1822 H2S tray_now override working with resolved mappings
