Replace the generated cmd.exe + robocopy update helper — which silently
failed on some machines — with an in-app C# installer:
* Stage the new version to a per-user temp folder off the install and run
the new RemSound.exe from there, so nothing in the install is locked by
the updater itself.
* Wait for the old process to fully exit (real WaitForExit), then
back-up-and-swap files in C# with retry + rename-aside; roll the install
back to the previous version on any failure, so a failed update can never
leave a half-installed RemSound.
* Log every step to updater.log; clean up old stages and legacy batch
artefacts on launch. Removed the old BuildInstallScript batch generator.
Route the "RemSound is already running" dialog and its follow-up message
through ForegroundDialog so they surface in front from a background-relaunched
copy, matching the earlier post-update fix.
Docs: rewrite the readme update sections for the new mechanism, regenerate
MANUAL.md, refresh the About-box changelog and RELEASE_NOTES.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
