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/Sources/VoiceCatCore/Feedback/SoundEvent.swift

@@ -0,0 +1,43 @@
+// SoundEvent — the cross-platform set of audible event cues. Each maps to a WAV bundled as an
+// SPM resource (Sources/VoiceCatCore/Sounds/, copied from assets/sounds/). The same logical set
+// is mirrored in the Windows client (clients/windows/.../Notifications/SoundEvent.cs) so feedback
+// stays consistent across platforms.
+
+import Foundation
+
+public enum SoundEvent: CaseIterable, Sendable {
+    case channelJoin    // another user joined my channel
+    case channelLeave   // another user left my channel
+    case channelRecv    // channel text message from someone else
+    case channelSent    // channel text message I sent
+    case pmRecv         // private message received
+    case pmSent         // private message I sent
+    case login          // connected / authenticated
+    case logout         // clean disconnect
+    case connectionLost // unexpected disconnect
+    case voiceOn        // my microphone stream started
+    case voiceOff       // my microphone stream stopped
+    case vaStart        // my voice-activity began (off by default)
+    case vaStop         // my voice-activity ended (off by default)
+    case ptt            // push-to-talk engaged (off by default)
+
+    /// Resource name (without extension) as bundled in Sources/VoiceCatCore/Sounds/.
+    var resourceName: String {
+        switch self {
+        case .channelJoin:    return "channel_join"
+        case .channelLeave:   return "channel_leave"
+        case .channelRecv:    return "channel_recv"
+        case .channelSent:    return "channel_sent"
+        case .pmRecv:         return "pm_recv"
+        case .pmSent:         return "pm_sent"
+        case .login:          return "login"
+        case .logout:         return "logout"
+        case .connectionLost: return "connection_lost"
+        case .voiceOn:        return "voice_on"
+        case .voiceOff:       return "voice_off"
+        case .vaStart:        return "va_start"
+        case .vaStop:         return "va_stop"
+        case .ptt:            return "ptt"
+        }
+    }
+}