feat(ui): add bundled custom notification sounds

Adds three embedded WAV files as additional notification sound choices
(ids 17-19) alongside the existing 16 game sounds. Playback via NAudio
WaveOutEvent/WinMM, which works correctly on Wine/Linux.

HellionChat/Plugin.cs

@@ -115,6 +115,7 @@ public sealed class Plugin : IAsyncDalamudPlugin
     internal Themes.ThemeRegistry ThemeRegistry { get; private set; } = null!;
     internal Ui.StatusBar StatusBar { get; private set; } = null!;
     internal Integrations.HonorificService HonorificService { get; private set; } = null!;
+    internal Integrations.CustomAudioPlayer CustomAudioPlayer { get; private set; } = null!;
 
     // Platform indirection over Dalamud.Utility.Util. Wired in Phase-1 ctor so
     // any service allocated in LoadAsync can read Plugin.PlatformUtil.
@@ -286,6 +287,7 @@ public sealed class Plugin : IAsyncDalamudPlugin
         TypingIpc = _host.Services.GetRequiredService<TypingIpc>();
         ExtraChat = _host.Services.GetRequiredService<ExtraChat>();
         HonorificService = _host.Services.GetRequiredService<Integrations.HonorificService>();
+        CustomAudioPlayer = _host.Services.GetRequiredService<Integrations.CustomAudioPlayer>();
         StatusBar = _host.Services.GetRequiredService<Ui.StatusBar>();
         MessageManager = _host.Services.GetRequiredService<MessageManager>();
         AutoTellTabsService = _host.Services.GetRequiredService<AutoTellTabsService>();