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/config/app_config.h

@@ -17,6 +17,7 @@ struct ProclamationConfig {
     int font_size = 32;                   // font size in pt
     std::string current_id = "";          // currently active proclamation ID
     bool schedule_active = false;         // follow the portal's listening schedule
+    bool schedule_enabled = true;         // local Schedule on/off toggle (default on)
 };
 
 struct AppConfig {