v3.9.1: plain/WASAPI streams now play on an ASIO-mode receiver (silent-mic fix)

Receiver: a Mixed (plain) session is rendered on an active lane in BothIndependent mode instead of being skipped, so a WASAPI-only sender is no longer silent to a receiver that has an ASIO driver selected. Also port the per-session buffer depth-drain (stops the receive jitter buffer bloating).

Sender: add sndAudFr meter (audio frames actually sent) to localise capture vs send.

App: startup sound cue (machine-wide, Preferences); stop sending audio when no peer is reachable (issue #8). Version 3.9.1.

Server (relay): fix updater version-compare for multi-dot tags, guard the main loop against crashes, reject spoofed BYE from a mismatched endpoint.

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

src/RemSound.App/AboutDialog.cs

@@ -20,6 +20,21 @@ internal sealed class AboutDialog : Form
     /// updates" path.</summary>
     private const string ReleaseNotes =
         """
+        RemSound v3.9
+
+        Listening for a long time no longer slowly builds up
+        delay. On the standard (non-ASIO) path the incoming audio
+        buffer used to creep deeper after a network hiccup and
+        never settle back, so a connection that started tight
+        could feel laggy by morning. It now eases itself back to
+        your chosen latency, gently and silently, so a long
+        session stays as tight as it began.
+
+        RemSound's log now also records whether your microphone
+        audio is actually leaving the machine, alongside how loud
+        it is — so a "my mic isn't getting through" report can be
+        pinned down from the log instead of guessed at.
+
         RemSound v3.8
 
         You can now start a brand-new profile at any time. A