Implement Phase 1: Global hotkey, HUD, and audio capture

Add complete listening UX without STT:
- Global hotkey manager with ⌘⇧V, push-to-talk and toggle modes
- Floating HUD with real-time RMS audio visualization
- AVAudioEngine capture with 16kHz mono PCM conversion
- 10-minute dictation timeout with ESC cancellation
- Optional start/stop sounds and microphone permissions
- Permission management for accessibility and input monitoring

All Phase 1 acceptance criteria met.

Sources/App/SoundManager.swift

@@ -0,0 +1,51 @@
+import Foundation
+import AVFoundation
+import AppKit
+import CoreUtils
+
+public class SoundManager: ObservableObject {
+    private let logger = Logger(category: "SoundManager")
+
+    @Published public var soundsEnabled: Bool = true
+
+    private var startSound: AVAudioPlayer?
+    private var stopSound: AVAudioPlayer?
+
+    public init() {
+        setupSounds()
+    }
+
+    private func setupSounds() {
+        // Use system sounds for now
+        // In a future version, we could bundle custom sound files
+        setupSystemSounds()
+    }
+
+    private func setupSystemSounds() {
+        // We'll use NSSound for system sounds since AVAudioPlayer requires files
+        // These are just placeholders - in a real implementation we'd bundle sound files
+        logger.info("Sound manager initialized with system sounds")
+    }
+
+    public func playStartSound() {
+        guard soundsEnabled else { return }
+
+        logger.debug("Playing start sound")
+        // Use a subtle system sound for start
+        NSSound(named: "Glass")?.play()
+    }
+
+    public func playStopSound() {
+        guard soundsEnabled else { return }
+
+        logger.debug("Playing stop sound")
+        // Use a different system sound for stop
+        NSSound(named: "Blow")?.play()
+    }
+
+    public func playErrorSound() {
+        logger.debug("Playing error sound")
+        // Always play error sound regardless of settings
+        NSSound(named: "Funk")?.play()
+    }
+}