Covers _validate_pin_key (all groups + negatives), _apply_pins_to_raw
(fonts list/tuple/typeerror, multi-pin, no-mutation, unknown-key guard),
and generate_profile (determinism, seed coercion, pin propagation through
to_prefs_dict, frozen-instance, dark_theme bool coercion, fonts list
roundtrip, int31 boundary). Includes a guard test that every dotted pin
key has a _PIN_TO_RAW mapping.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
