Extends Clock_IncMS()'s existing sec->min->hour cascade to also roll
day->month->year (with leap-year Feb 29 via Days_In_Month()), and adds
Clock_RecalcWeekday() computing current_weekday via Zeller's congruence
whenever the date changes, rather than trusting PCF8563's own weekday
register (which would drift if the date is edited manually). Verified
the formula against 2026-07-31, a known Friday.
Adds KEY_EVENT_SECOND_TICK, generated once per real second from
Clock_IncMS() via a new second_tick_flag and pushed through the normal
event queue, so every foreground App's onEvent() receives it and
decides independently whether to act. Removes the old global
inactivity_timer (60s sleep from anywhere) entirely. HomeApp now
accumulates its own idle-second counter and sleeps after 10s idle
specifically while on the home screen; MenuApp's existing 10s
auto-close is converted from onRun() polling to the same tick+reset
pattern for consistency. Any non-tick key event resets each app's own
counter to 0.
