feat(clients): event sound effects + optional text-to-speech

Add audible cues and optional spoken announcements for session events
(join/leave, channel + PM sent/recv, login, logout/connection-lost,
mic on/off, voice-activity, PTT) across all three clients, driven off
the shared C ABI vc_event stream so the mapping stays consistent.

TTS is off by default; when enabled it announces events and reads
message/PM bodies aloud. Master toggles + a sound-volume slider; the
per-utterance voice-activity and PTT cues default off. WAVs ship from
assets/sounds/.

Windows (built + verified): new VoiceCat.App/Notifications/ layer
(FeedbackSettings -> %AppData%\VoiceCat\feedback.json, SoundPlayerPool
via System.Media.SoundPlayer, SpeechAnnouncer via Prismatoid 0.3.0,
EventFeedback dispatcher); MainForm hooks; NotificationSettingsForm
under Settings > Notifications; csproj adds the Prismatoid PackageRef
and copies the WAVs into sounds\.

macOS + iOS (written, not yet built -- needs a Mac): shared
VoiceCatCore/Feedback/ (SoundEvent, EventFeedback = AVAudioPlayer pool
+ native AVSpeechSynthesizer, FeedbackSettings over UserDefaults); WAVs
bundled via Package.swift resources (.process). Hooks in SessionState/
AppState (iOS) and MainWindowController (macOS); settings UI in
SettingsView (iOS) and SettingsWindowController (macOS).

No core/server code touched; ctest --preset dev unaffected.

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

clients/windows/VoiceCat.App/Notifications/FeedbackSettings.cs

@@ -0,0 +1,55 @@
+using System.Text.Json;
+
+namespace VoiceCat.App.Notifications;
+
+/// <summary>
+/// User preferences for event sounds and spoken (text-to-speech) feedback. Persisted to
+/// %AppData%\VoiceCat\feedback.json — same pattern as <see cref="Models.ServerListStore"/>:
+/// a missing or corrupt file yields defaults rather than throwing.
+/// </summary>
+public sealed class FeedbackSettings
+{
+    /// <summary>Master switch for event sound effects.</summary>
+    public bool Sounds { get; set; } = true;
+
+    /// <summary>Master switch for spoken announcements (Prismatoid TTS). Off by default.</summary>
+    public bool Speech { get; set; } = false;
+
+    /// <summary>Sound-effects volume, 0..1. 0 mutes effects (SoundPlayer has no gain control,
+    /// so this is honoured as a mute gate — see <see cref="SoundPlayerPool"/>).</summary>
+    public float Volume { get; set; } = 1.0f;
+
+    /// <summary>Play va_start/va_stop for your own voice-activity transitions. Off by default
+    /// (fires on every utterance — noisy).</summary>
+    public bool SelfTalkSounds { get; set; } = false;
+
+    /// <summary>Play the ptt cue when push-to-talk is engaged. Off by default.</summary>
+    public bool PttSound { get; set; } = false;
+
+    private static readonly JsonSerializerOptions JsonOptions = new() { WriteIndented = true };
+
+    private static string AppDataDir => Path.Combine(
+        Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "VoiceCat");
+
+    private static string FilePath => Path.Combine(AppDataDir, "feedback.json");
+
+    public static FeedbackSettings Load()
+    {
+        try
+        {
+            if (!File.Exists(FilePath)) return new FeedbackSettings();
+            string json = File.ReadAllText(FilePath);
+            return JsonSerializer.Deserialize<FeedbackSettings>(json) ?? new FeedbackSettings();
+        }
+        catch
+        {
+            return new FeedbackSettings();
+        }
+    }
+
+    public void Save()
+    {
+        Directory.CreateDirectory(AppDataDir);
+        File.WriteAllText(FilePath, JsonSerializer.Serialize(this, JsonOptions));
+    }
+}