Adds the auxcnc W axis to the front-page Position table:
- axis-vars.js exposes a 'w' computed property fed by state.aux_pos /
aux_enabled / aux_homed / aux_present (set by AuxAxis on the host).
No motor mapping, no soft-limit warnings - the aux controller does
its own bounds.
- control-view.pug adds a W row after the xyzabc loop. The Set/Zero
button calls /api/aux/set-zero {mm:0} and the Home button calls
/api/aux/home, which hit the new endpoints exposed by Web.py.
- control-view.js: aux_home(), aux_set_zero(), and aux_jog() helpers.
When aux_enabled is false (no aux.json or aux.json has enabled=false)
the row stays hidden, matching the existing axis-row behavior.
