v0.6.3

Install and restart now works on Windows too (part of 0.6.3)

The Windows app downloads the installer of the new version, checks size
and SHA-256 (required, the file is run) and that it is a Windows program,
then update.bat waits for the app to quit, runs the Inno installer quietly
(per-user, no admin) and starts SeekSync again. Folders SeekSync can't
write to keep the release page route. Docs, guide and changelog updated;
tests use a fake installer.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>