v1.2.1

v1.2.1: independent-audit fix batch (10 fixes + 2 tests)

Packaging: wheels now ship assets/fonts/* (glob didn't descend — verified
via wheel build); Dockerfile installs editable to mirror CI, closing the
clean-clone trap where lrelease ran after the wheel was built; stale local
egg-info removed.

Functional: exclusive theme QActionGroup; real :hover background (Qt QSS
has no opacity); stop-line geometry — cars queued beyond the crosswalk
(_STOP_LINE_M=11) and stop lines painted; serial write_timeout 1s->0.1s
caps GUI stalls from a wedged adapter; from_json rejects NaN/Infinity
durations; spacebar no longer unpauses during a quiz; speed label format
unified to :.1f.

Tests: 146 total — NaN rejection, install_fonts family coverage (path was
previously untested, which is why the wheel bug survived), panel label
expectation updated. Green locally and in Docker.