v3.4: handle-leak fix, Realtek ASIO block, device notifications, quick profile switch, hotkey announcements

Freezes the v3.4 feature set (everything since the v3.3 public release):

- Fix the receiver handle leak: the 3-second device-refresh timer reopened the
  configured ASIO driver every tick, and Realtek's ASIO driver leaks Event+Mutant
  handles on every open. Cache the ASIO probe per driver so it is opened once.
- Realtek ASIO block: detect a Realtek ASIO driver, offer once to disable it, and
  never touch it again if disabled; Options-menu toggle to reverse. Global config.
- Device hot-plug is event-driven (AudioDeviceChangeNotifier) instead of a 3s poll;
  debounced refresh, falls back to polling if registration fails.
- Quick profile switch: new global hotkey opens an NVDA-friendly popup of all
  profiles (current marked); Enter/click switches; plays a new "profile menu open"
  cue with Preferences mute + custom-sound.
- Announce assigned global hotkeys on the controls/menu items they drive (NVDA reads
  "press X anywhere"). File > Open already had Ctrl+O.
- Held-back changes folded in: config-folder migration, codec-column fix, Tailscale
  endpoint network-prune, empty-password guard, and the handle-leak diagnostics
  (ProcessSelfMeter, HandleTypeProbe).

Version bumped to 3.4.0.

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

src/RemSound.App/AudioDeviceChangeNotifier.cs

@@ -0,0 +1,47 @@
+using NAudio.CoreAudioApi;
+using NAudio.CoreAudioApi.Interfaces;
+
+namespace RemSound.App;
+
+/// <summary>
+/// Fires a callback whenever the set of Windows audio endpoints changes — a device is added,
+/// removed, changes state (plugged / unplugged / enabled / disabled), or the default device
+/// changes. This replaces the pre-v3.4 3-second polling of the device lists: instead of
+/// re-enumerating every tick whether or not anything changed, RemSound re-reads the device lists
+/// only when Windows actually tells us the device set changed.
+///
+/// The callbacks arrive on a COM thread, so the consumer (<see cref="MainForm"/>) marshals to the
+/// UI thread and debounces — a single hot-plug typically fires several of these in quick
+/// succession (state-changed + added + default-changed), which collapse into one refresh.
+///
+/// Property-value changes (volume nudges, format tweaks) are deliberately ignored: they fire
+/// constantly and never change the device <em>set</em>, so reacting to them would defeat the
+/// whole point of going event-driven.
+/// </summary>
+internal sealed class AudioDeviceChangeNotifier : IMMNotificationClient, IDisposable
+{
+    private readonly MMDeviceEnumerator enumerator = new();
+    private readonly Action onChange;
+    private bool registered;
+
+    public AudioDeviceChangeNotifier(Action onChange)
+    {
+        this.onChange = onChange;
+        enumerator.RegisterEndpointNotificationCallback(this);
+        registered = true;
+    }
+
+    public void OnDeviceStateChanged(string deviceId, DeviceState newState) => onChange();
+    public void OnDeviceAdded(string pwstrDeviceId) => onChange();
+    public void OnDeviceRemoved(string deviceId) => onChange();
+    public void OnDefaultDeviceChanged(DataFlow flow, Role role, string defaultDeviceId) => onChange();
+    public void OnPropertyValueChanged(string pwstrDeviceId, PropertyKey key) { /* ignore — too chatty, no set change */ }
+
+    public void Dispose()
+    {
+        try { if (registered) enumerator.UnregisterEndpointNotificationCallback(this); }
+        catch { /* COM teardown race on shutdown — harmless */ }
+        registered = false;
+        try { enumerator.Dispose(); } catch { /* ignore */ }
+    }
+}