The panel_switch_anim system already flashes the active panel
border from theme.info to theme.accent on focus change
(switch_focus). Add an explicit test that verifies the
animation reset-on-switch and the tick-by-tick advance back
to 100, guarding against future refactors breaking the
visual feedback for Tab panel switching.
Tests: 1403 pass (was 1402), zero warnings.
vasilito
75c3a472df