feat(chat): volume control for inline audio clips

Add a per-clip volume slider plus a master volume control with a
"Universal volume" toggle in the chat header.

- ClipPlayer gains a SetVolume command; the worker remembers gain across
  clips and reapplies it to each freshly connected player.
- New config.clip_volume (universal level) and config.clip_volume_universal
  (mode toggle, default on), both persisted; old configs load at unity in
  universal mode.
- Universal on: master and per-clip sliders drive one shared level applied
  to every clip. Universal off: each clip keeps its own in-memory level and
  the master slider is inert.
- play_ready_audio applies the resolved effective gain right after Play.

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

src/audio/clip_player.rs

@@ -40,6 +40,7 @@ enum ClipCommand {
     Resume,
     Seek(Duration),
     Stop,
+    SetVolume(f32),
 }
 
 /// Cheap, `Send` command handle for the dedicated playback thread.
@@ -51,13 +52,16 @@ pub struct ClipPlayer {
 impl ClipPlayer {
     /// Start the playback worker. The system output device is opened lazily on
     /// first Play, so merely launching PeerSpeak never claims another stream.
-    pub fn new() -> (Self, SharedClipStatus) {
+    ///
+    /// `initial_volume` is the universal gain (`1.0` = unity) applied to every
+    /// clip, restored from config so the level persists across sessions.
+    pub fn new(initial_volume: f32) -> (Self, SharedClipStatus) {
         let (command_tx, command_rx) = mpsc::channel();
         let status = Arc::new(Mutex::new(ClipStatus::default()));
         let worker_status = Arc::clone(&status);
         std::thread::Builder::new()
             .name("peerspeak-clip-player".to_string())
-            .spawn(move || playback_worker(command_rx, worker_status))
+            .spawn(move || playback_worker(command_rx, worker_status, initial_volume))
             .expect("failed to spawn clip playback thread");
         (
             Self {
@@ -94,11 +98,24 @@ impl ClipPlayer {
     pub fn stop(&self) {
         let _ = self.command_tx.send(ClipCommand::Stop);
     }
+
+    /// Set the universal playback gain (`1.0` = unity). Applies to the current
+    /// clip immediately and to every clip played afterwards.
+    pub fn set_volume(&self, volume: f32) {
+        let _ = self.command_tx.send(ClipCommand::SetVolume(volume));
+    }
 }
 
-fn playback_worker(command_rx: mpsc::Receiver<ClipCommand>, status: SharedClipStatus) {
+fn playback_worker(
+    command_rx: mpsc::Receiver<ClipCommand>,
+    status: SharedClipStatus,
+    initial_volume: f32,
+) {
     let mut output: Option<MixerDeviceSink> = None;
     let mut player: Option<Player> = None;
+    // Universal gain remembered across clips so a level set on one upload
+    // carries to the next; reapplied to each freshly connected player.
+    let mut volume = initial_volume.max(0.0);
 
     loop {
         match command_rx.recv_timeout(Duration::from_millis(100)) {
@@ -124,7 +141,9 @@ fn playback_worker(command_rx: mpsc::Receiver<ClipCommand>, status: SharedClipSt
                 if output.is_none() {
                     match DeviceSinkBuilder::open_default_sink() {
                         Ok(sink) => {
-                            player = Some(Player::connect_new(sink.mixer()));
+                            let new_player = Player::connect_new(sink.mixer());
+                            new_player.set_volume(volume);
+                            player = Some(new_player);
                             output = Some(sink);
                         }
                         Err(error) => {
@@ -177,6 +196,12 @@ fn playback_worker(command_rx: mpsc::Receiver<ClipCommand>, status: SharedClipSt
                 }
                 reset(&status);
             }
+            Ok(ClipCommand::SetVolume(level)) => {
+                volume = level.max(0.0);
+                if let Some(player) = player.as_ref() {
+                    player.set_volume(volume);
+                }
+            }
             Err(mpsc::RecvTimeoutError::Disconnected) => break,
             Err(mpsc::RecvTimeoutError::Timeout) => {}
         }