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/apple/iOS/VoiceCatiOS/Views/SettingsView.swift

@@ -8,6 +8,14 @@ struct SettingsView: View {
     @StateObject private var router = IOSAudioRouter.shared
     @State private var showAdvanced = false
 
+    // Notification feedback prefs — keys shared with VoiceCatCore's FeedbackSettings, so the
+    // EventFeedback player reads the same values these toggles write.
+    @AppStorage("feedback.sounds")   private var soundsEnabled = true
+    @AppStorage("feedback.speech")   private var speechEnabled = false
+    @AppStorage("feedback.volume")   private var soundsVolume = 1.0
+    @AppStorage("feedback.selfTalk") private var selfTalkEnabled = false
+    @AppStorage("feedback.ptt")      private var pttSoundEnabled = false
+
     var body: some View {
         NavigationStack {
             Form {
@@ -217,6 +225,27 @@ struct SettingsView: View {
                     }
                 }
 
+                // MARK: - Notifications
+                Section("Notifications") {
+                    Toggle("Event sounds", isOn: $soundsEnabled)
+                        .accessibilityLabel("Play event sounds")
+                    if soundsEnabled {
+                        VStack(alignment: .leading, spacing: 4) {
+                            Text("Sound volume")
+                                .font(.caption)
+                            Slider(value: $soundsVolume, in: 0...1)
+                                .accessibilityLabel("Sound volume")
+                        }
+                    }
+                    Toggle("Speak events (text-to-speech)", isOn: $speechEnabled)
+                        .accessibilityLabel("Speak events")
+                        .accessibilityHint("Announces joins and leaves and reads message text aloud.")
+                    Toggle("Your own voice-activity sounds", isOn: $selfTalkEnabled)
+                        .accessibilityLabel("Voice activity sounds")
+                    Toggle("Push-to-talk cue", isOn: $pttSoundEnabled)
+                        .accessibilityLabel("Push to talk cue")
+                }
+
                 // MARK: - Admin
                 if session.permissions.canAdminAccounts || session.permissions.isAdmin {
                     Section("Administration") {