fix: exempt the stability calibration from the consumer-values check

[koen-vg]

tools/calibrate stability cannot build its DAG on current main:

RuntimeError: Validation failed:
 - consumer_values: base config enables food_utility_piecewise but configured
   consumer values baseline scenario '_cal_baseline_iter00' is not defined

#38 replaced the lax consumer-values check with a stricter one that requires
consumer_values.baseline_scenario to name a declared scenario. That is the
right rule for ordinary configs, but the deviation-penalty calibration drives
its solves in-process: calibrate_deviation_penalty.py synthesizes
_cal_baseline_iterNN / _cal_main_iterNN per Broyden iteration and passes
them straight to build_scenario_entry. They are never Snakemake scenarios,
so the placeholder in config/calibration/stability.yaml has nothing to
resolve against.

Skipping the check when deviation_penalty.calibration.generate is set follows
the is_generation_run convention already used by the provenance validator.
Declaring the placeholder in scenarios: instead would have leaked a phantom
scenario into list_scenarios().

Found while re-checking calibration fingerprints after #38; regression test
added.