Bump to v3.1.2: tray icon re-stamps on state change, recording shows as a flag

- Tray icon now re-registers itself (hide+re-show) whenever the meaningful
  state changes — peer connect/drop, send/receive toggle, recording
  start/stop — so the name a screen reader announces stays in step with
  the live state. Fixes the persistent "no peers" then "1 peer" double
  announcement that the old "show window then minimise again" trick used
  to clear by hand. Same root cause as the v3.1.1 stuck-tooltip fix, just
  exposed when the state changes a moment after the icon appears.
- Recording shows as a plain "recording" flag in the tray rather than a
  live timer. A ticking timer would have either flickered the icon once a
  second or left a screen reader announcing a stale time next to the live
  one. Removed the now-dead FormatRecordingElapsed helper.
- Bundles the earlier Win7 updater fix (6cbde0d): a failed secure
  connection is no longer mislabelled as "you're up to date".
- About box, RELEASE_NOTES.md, readme.html and MANUAL.md updated to match.

Co-Authored-By: Claude Opus 4.8 <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>3.1.1</Version>
+    <Version>3.1.2</Version>
   </PropertyGroup>
 
   <ItemGroup>