calibration: make Calibrate All MPC-aware

[ozharsky]

Summary

Make Calibrate All MPC-aware. _CALIBRATE_ALL_STEP_2 currently hardcodes PID_CALIBRATE, which destroys the MPC model and — because SAVE_CONFIG writes control = pid — leaves MPC-only options invalid, so klippy halts at parse (Option 'heater_power' is not valid in section 'extruder').

Changes

• meta-opencentauri/recipes-apps/klipper/files/calibration.cfg — the extruder step of _CALIBRATE_ALL_STEP_2 runs MPC_CALIBRATE when printer.configfile.settings.extruder.control == 'mpc', and the unchanged PID_CALIBRATE otherwise.

Why this shape

• Two functional lines, single purpose; PID behaviour is unchanged (|default('pid') guards any config without the key).
• Mirrors logic running on a CC1 since 2026-10-03 as a config override, where Calibrate All now completes with control = mpc intact.

Test plan

• CI build passes.
• MPC printer: Calibrate All → control = mpc persists; klippy restarts cleanly.
• PID printer: behaviour unchanged.

Fixes #407