Add build-and-test suite (in-app self-test + publish gate); fix release-zip missing sounds

The test suite, modelled on Andre's Sensor Readout (an in-app self-test + a build
script), runnable as one step before every publish.

Part 1 - in-app multi-step self-test (SelfTest.cs), run by --selftest:
  audio round-trip (PCM + Opus over localhost, dedicated test port so it never
  clashes with a running instance), encryption right/wrong-password + fingerprint,
  packet framing + malformed rejection, client<->server wire-format compatibility,
  settings save/reload, profile save/reload (temp folder), diagnostics-report
  privacy (never leaks a password), and bundled-resources present. Each step is
  timed and reported PASS/FAIL/SKIP; exit 0 only if nothing failed. Replaces the
  old single-shot --selftest. RunDiagnostics refactored to expose
  BuildDiagnosticsReport(AppConfig) for the privacy step.

Part 2 - run-tests.ps1: builds, then checks the package (sounds, readme, native
  opus, framework-dependent, dll version == csproj), the About-box changelog, the
  client/server wire contract (relay magic/version/port still match RemPacket),
  the CLI surface, and runs --selftest. build-release.ps1 now runs this gate first
  and aborts the release if it fails.

Bug caught + fixed: the published release zip carried ZERO cue sounds (startup
  sound + connect/disconnect/etc.) - MSBuild's incremental Content-copy marker
  skipped sounds\ on a fresh publish. Added an AfterTargets=Publish copy in the
  csproj that lands every cue WAV in the published sounds\ folder regardless of
  the marker. Verified: a staging publish now contains all 9 cue WAVs.

Manual/help: --selftest description updated (readme.html + MANUAL.md).

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

src/RemSound.App/RemSound.App.csproj

@@ -119,4 +119,21 @@
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
   </ItemGroup>
+
+  <!-- Guarantee the cue WAVs land in a PUBLISHED build. The sounds\ Content items above use
+       CopyToOutputDirectory=PreserveNewest, but MSBuild's incremental "copy already done" marker
+       (obj\...\.csproj.CopyComplete) can skip that copy when publishing into a fresh output folder
+       whose marker is up to date — which silently shipped the v3.9 zip with NO cue sounds at all
+       (startup sound + connect/disconnect/record/etc.). This explicit post-publish copy is marker-
+       independent: it always copies every WAV from the source sounds\ folder into the published
+       sounds\ folder. Build-release.ps1 zips the publish output, so this is what makes the release
+       reliably contain the sounds. (The self-test "Bundled resources present" step verifies it.) -->
+  <Target Name="EnsureCueSoundsPublished" AfterTargets="Publish">
+    <ItemGroup>
+      <_CueWavs Include="..\..\sounds\*.wav" />
+    </ItemGroup>
+    <Copy SourceFiles="@(_CueWavs)"
+          DestinationFolder="$(PublishDir)sounds"
+          SkipUnchangedFiles="false" />
+  </Target>
 </Project>