Bump to v1.2.0: recording, sound cues, drift compensation, diagnostics

New user-facing features:

* Recording. Dedicated Record menu (Alt+O — moved from Alt+R to
  avoid clashing with the Receive audio checkbox), Start/Stop on
  Ctrl+R, settings dialog, per-profile source / format / bit-depth /
  channel-mode / folder. Three source modes (received only, sent
  only, both). Files are crash-resilient — a process crash
  mid-recording leaves a playable file containing everything up to
  the last header refresh (~5 seconds).

* Four output formats, all functional:
    - WAV: 16/24-bit PCM or 32-bit float, custom writer with
      periodic RIFF re-patching.
    - MP3: LAME 128–320 kbps CBR (via NAudio.Lame).
    - OGG-Opus: 96–256 kbps VBR (via Concentus.Oggfile, reusing the
      Concentus encoder from the wire path).
    - FLAC: 16/24-bit lossless (via CUETools.Codecs.FLAKE — pure
      managed, no native DLL).

* Recording start/stop sound cues. record start.wav and
  record stop.wav play around the recording transition. Played via
  System.Media.SoundPlayer to the default Windows output, separate
  from the recording pipeline so a normal recording does not contain
  the cue.

* Per-cue Preferences. The old single "Mute connect/disconnect
  sounds" checkbox is replaced by a CheckedListBox: Connect /
  Disconnect / Recording start / Recording stop. Old profiles with
  the legacy MuteConnectionCues=true are honoured on first load via
  a migration path in the new Load* helpers.

* Receiver-side drift compensation switched from discrete
  single-frame splices to a continuous WdlResampler at a smoothed
  rate ratio. SessionPlayout.cs rewrite.

Diagnostics (only active with Enable logs ticked):

* Per-stage discontinuity probes — sender raw capture (per backend,
  PushModeWasapi + Asio both wired), sender pre-encode (now per
  lane in BothIndependent, fixing a cross-stream artefact), receiver
  post-decode, post-ring, post-resampler.

* Wire-level packet sequence tracking on each PCM stream — in-order
  / missed / reordered / duplicated counts in the diag log.

* Clipped-sample delta in the diag log.

* New AudioStepProbe in RemSound.Core with per-channel scan helper.

UI changes:

* Record menu uses Alt+O (Rec&ord). Inside the menu, item mnemonics
  unchanged (S / T / O / C).

* Auto-tune interval combo label is mode-aware: "Auto-tune latency
  interval" in classic modes, "Auto-tune interval — WASAPI and ASIO"
  in BothIndependent. The combo's Enabled state now follows EITHER
  lane's auto-tune checkbox (was only the WASAPI one — bug).

Wire format and audio pipeline unchanged from v1.1 — v1.1 and v1.2
peers interoperate.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/RemSound.App/RemSound.App.csproj

@@ -14,7 +14,7 @@
          tag_name on the latest GitHub release; bump it on every public release. The
          AssemblyVersion / FileVersion default to this value, and Assembly.GetName().Version
          is what the About dialog and the updater both read. -->
-    <Version>1.1.0</Version>
+    <Version>1.2.0</Version>
   </PropertyGroup>
 
   <ItemGroup>
@@ -22,6 +22,17 @@
     <ProjectReference Include="..\RemSound.Sender\RemSound.Sender.csproj" />
     <ProjectReference Include="..\RemSound.Receiver\RemSound.Receiver.csproj" />
     <PackageReference Include="NAudio" Version="2.3.0" />
+    <!-- LAME wrapper for MP3 encoding. Pulled in for the recording feature. The native
+         libmp3lame.dll ships with the package and is copied to the output folder. -->
+    <PackageReference Include="NAudio.Lame" Version="2.1.0" />
+    <!-- OGG container writer that wraps Concentus-encoded Opus. Same Concentus the wire
+         path already uses (transitive dep), so the recording-side OGG-Opus output is
+         byte-for-byte the same encoder we'd send on a live Opus stream. -->
+    <PackageReference Include="Concentus.Oggfile" Version="1.0.7" />
+    <!-- Pure-managed FLAC encoder (Flake). Same encoder CUETools uses; no native DLL,
+         no P/Invoke. Lossless, ships as managed IL, smaller files than WAV (~50%) without
+         sample-data loss. -->
+    <PackageReference Include="CUETools.Codecs.FLAKE" Version="1.0.5" />
   </ItemGroup>
 
   <ItemGroup>
@@ -35,6 +46,16 @@
       <Link>disconnect.wav</Link>
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
+    <!-- Recording start/stop cues. Filenames contain a space — preserve on copy so the
+         load-by-filename path in TryLoadCueSound finds them exactly as written. -->
+    <Content Include="..\..\record start.wav">
+      <Link>record start.wav</Link>
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+    <Content Include="..\..\record stop.wav">
+      <Link>record stop.wav</Link>
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
     <!-- User manual. F1 anywhere in the app opens this via the user's default browser
          (HelpLauncher.OpenManual). The PreserveNewest mode means a fresh publish overwrites
          the published copy whenever the source is newer; manually-edited copies inside