Add audio deps; extract input handling to threads

Add ALSA and Rodio crates to Cargo.toml and lockfile to enable audio
playback.
Update Nix expressions to include `alsa-lib` as a build input.
Refactor input event handling into a new `app::threads` module:
 - Define `AppEvent` enum and `handle_input_events` function there.
 - Adjust imports in `app/app.rs` and `main.rs` accordingly.
   Remove the now‑unused `handle_input_events` and `AppEvent`
   definitions from
   `app/app.rs`.

src/app/threads/events.rs

@@ -0,0 +1,6 @@
+use ratatui::crossterm::event::KeyEvent;
+
+pub enum AppEvent {
+    Input(KeyEvent),
+    Resize(u16, u16),
+}

src/app/threads/handle_input_events.rs

@@ -0,0 +1,24 @@
+use crate::app::threads::AppEvent;
+use ratatui::crossterm::event::{Event, read};
+use std::sync::mpsc::Sender;
+
+pub fn handle_input_events(tx: Sender<AppEvent>) {
+    loop {
+        match read() {
+            Ok(ev) => match ev {
+                Event::Key(key) => {
+                    if tx.send(AppEvent::Input(key)).is_err() {
+                        break;
+                    }
+                }
+                Event::Resize(c, r) => {
+                    if tx.send(AppEvent::Resize(c, r)).is_err() {
+                        break;
+                    }
+                }
+                _ => {}
+            },
+            Err(_) => continue,
+        }
+    }
+}

src/app/threads/mod.rs

@@ -0,0 +1,5 @@
+pub mod events;
+pub mod handle_input_events;
+
+pub use events::AppEvent;
+pub use handle_input_events::handle_input_events;