Warn when a driver's transponder collides with a different driver

Registering or editing a driver with a transponder already assigned
to a different driver (e.g. a wrong-class typo) previously saved
silently - the only symptom was that driver's laps never registering
during their heat, with no indication why. Now a confirm dialog names
the conflicting driver and their class before saving; the same
person's own multiple class entries sharing one physical transponder
are correctly never flagged.

Also confirms two things the user asked to verify: the race clock
already counts down for all timed session types (only open practice
counts up unbounded), and a driver not entered in a heat already has
their laps fully discarded rather than recorded - both were already
correct, no changes needed there.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/run.js

@@ -1,3 +1,4 @@
+import "./driver_profile_logic.test.js";
 import "./training_logic.test.js";
 import "./public_training_profile.test.js";
 import "./race_timing_logic.test.js";