Refactor App to use unified AppChannels for events

App now receives an AppChannels struct; AppEvent enum removed.

Event handling, tick generation, and audio communication are now
performed through dedicated channels.

src/app/threads/mod.rs

@@ -1,7 +1,9 @@
+mod app_channels;
 mod audio;
 mod events;
 mod tick;
 
+pub use app_channels::AppChannels;
 pub use audio::{AudioCmd, SoundrackParts, Soundtrack, handle_audio};
-pub use events::{AppEvent, handle_events};
-pub use tick::spawn_tick_thread;
+pub use events::handle_ct_events;
+pub use tick::handle_tick_event;