Remove AppChannels, use separate receivers

Refactor App::run to accept individual Receiver arguments instead of an
AppChannels struct. Delete the AppChannels definition and its re‑export,
and update main.rs to create each channel manually and pass the
receivers
to App::run. Rename the CLI field `sound_track` to `soundtrack` and
adjust
all references. Clean up imports and formatting accordingly.

src/cli.rs

@@ -148,7 +148,7 @@ pub struct Cli {
             default_value_t = Soundtrack::Default,
             value_enum
         )]
-    pub sound_track: Soundtrack,
+    pub soundtrack: Soundtrack,
 
     /// Mute soundtrack (default: disabled).
     #[arg(