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.Receiver/AudioReceiver.cs

@@ -832,6 +832,36 @@ public sealed class AudioReceiver : IDisposable
         return null;
     }
 
+    /// <summary>
+    /// The wire codec of the freshest currently-active receive session across all peers, or
+    /// null when nothing is being received. Surfaced in the SNAP log's Codec column so a
+    /// receive-only node reports what it is actually decoding rather than its dormant send-codec
+    /// setting (the old behaviour logged "Pcm" for a node receiving "PCM over Opus"). Lockless
+    /// scan for the freshest session, then a short lock to read its codec.
+    /// </summary>
+    public AudioTransportCodec? ActiveReceiveCodec
+    {
+        get
+        {
+            var now = DateTime.UtcNow;
+            SessionPlayout? freshest = null;
+            foreach (var sp in playoutEngine.ActiveSessions)
+            {
+                if (now - sp.LastWriteUtc > SessionIdleTimeout) continue;
+                if (freshest is null || sp.LastWriteUtc > freshest.LastWriteUtc) freshest = sp;
+            }
+            if (freshest is null) return null;
+            lock (sessionsLock)
+            {
+                if (sessions.TryGetValue((freshest.Endpoint, freshest.StreamId), out var session))
+                {
+                    return session.Codec;
+                }
+            }
+            return null;
+        }
+    }
+
     // === Packet routing (called on network thread) ===
 
     /// <summary>Hook for Heartbeat packets that arrive on the audio receiver's socket. The