feat: notification chimes for room join / peer join / peer leave (phase 1)

Adds audible notifications for the basic membership events: a bright ascending
triad when you join a room, a soft two-note rise when another participant
joins, and a two-note fall when one leaves. Hooked into the app's UiEvent
handling (RoomJoined / PeerJoined / PeerLeft) so each is played locally by
whoever observes the event.

The chimes are short mono 16-bit WAVs generated by a committed stdlib-only
Python script (assets/sounds/generate_chimes.py) and embedded in the binary
with include_bytes!, so a deployed single binary is self-contained. The new
notify module materializes each to a temp file once, then plays it
fire-and-forget via pw-play (PipeWire-native; falls back to paplay/aplay) on a
detached thread that waits on the child -- never blocks the UI, never leaves a
zombie, and silently no-ops if no player is available.

Phase 1 of a larger plan; always-on for now. Later phases: reconnect-attempt /
reconnected sounds, a settings enable/disable toggle, per-event custom sounds,
and extra events (self-leave, mute/unmute, connection-lost).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/notify.rs

@@ -0,0 +1,91 @@
+//! Notification chimes for room events (join / peer-join / peer-leave, with more
+//! events in later phases).
+//!
+//! The WAVs are embedded in the binary (`include_bytes!`) so a deployed single
+//! binary is self-contained — no asset directory to ship alongside it. On first
+//! use each sound is written once to a temp file, then played fire-and-forget
+//! via `pw-play` (PipeWire-native; falls back to `paplay`/`aplay`). Playback runs
+//! on a detached thread that waits on the child, so it never blocks the UI and
+//! never leaves a zombie. Any failure (no player, no audio) is silent by design —
+//! a missing chime should never disrupt a call.
+
+use std::collections::HashMap;
+use std::path::{Path, PathBuf};
+use std::process::{Command, Stdio};
+use std::sync::{Mutex, OnceLock};
+
+/// A notification event with a distinct chime.
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+pub enum Sound {
+    /// You joined a room.
+    SelfJoin,
+    /// Another participant joined.
+    PeerJoin,
+    /// A participant left.
+    PeerLeave,
+}
+
+impl Sound {
+    /// Embedded WAV bytes for this sound.
+    fn bytes(self) -> &'static [u8] {
+        match self {
+            Sound::SelfJoin => include_bytes!("../assets/sounds/self-join.wav"),
+            Sound::PeerJoin => include_bytes!("../assets/sounds/peer-join.wav"),
+            Sound::PeerLeave => include_bytes!("../assets/sounds/peer-leave.wav"),
+        }
+    }
+
+    /// Stable file stem for the cached temp file.
+    fn name(self) -> &'static str {
+        match self {
+            Sound::SelfJoin => "self-join",
+            Sound::PeerJoin => "peer-join",
+            Sound::PeerLeave => "peer-leave",
+        }
+    }
+}
+
+/// Play a notification chime, fire-and-forget. Never blocks; never errors out.
+pub fn play(sound: Sound) {
+    let Some(path) = cached_path(sound) else {
+        return;
+    };
+    std::thread::spawn(move || spawn_player(&path));
+}
+
+/// Materialize the embedded WAV to a temp file the first time it's needed and
+/// cache the path. Returns `None` only if the file can't be written.
+fn cached_path(sound: Sound) -> Option<PathBuf> {
+    static CACHE: OnceLock<Mutex<HashMap<&'static str, PathBuf>>> = OnceLock::new();
+    let cache = CACHE.get_or_init(|| Mutex::new(HashMap::new()));
+
+    let mut guard = cache.lock().unwrap();
+    if let Some(path) = guard.get(sound.name()) {
+        return Some(path.clone());
+    }
+    let path = std::env::temp_dir().join(format!("peerspeak-{}.wav", sound.name()));
+    if std::fs::write(&path, sound.bytes()).is_err() {
+        return None;
+    }
+    guard.insert(sound.name(), path.clone());
+    Some(path)
+}
+
+/// Try each available player in turn, waiting on the first that starts (which
+/// reaps the child). Runs on a detached thread, so the wait is harmless.
+fn spawn_player(path: &Path) {
+    for player in ["pw-play", "paplay", "aplay"] {
+        let started = Command::new(player)
+            .arg(path)
+            .stdin(Stdio::null())
+            .stdout(Stdio::null())
+            .stderr(Stdio::null())
+            .status();
+        // `status()` errors only if the player binary isn't present; on a real
+        // playback error it still returns (non-zero), so a started player ends
+        // the loop either way — we don't want to double-play through fallbacks.
+        if started.is_ok() {
+            return;
+        }
+    }
+}