Kiosk: apply schedule engine in playback and add System Settings toggle

ScrollerPage now resolves the active Block from ScheduleManager (reusing
the existing stream-switch path), honoring dynamicAudio true/false and
falling back to local selection for gaps, no schedule, or toggle off.
Adds a 'Schedule' On/Off entry (default On) in System Settings persisted
in config.yaml, and config plumbing (proclamation.schedule_enabled). All
on-device schedule times remain 12h AM/PM.

src/settings_menu.h

@@ -10,6 +10,7 @@ enum class SystemSettingId {
     EmailAddress,
     LicenseKey,
     SystemName,
+    Schedule,
     WiFiSetup,
     Timezone,
     DateFormat,