Use fakeroot when building .deb packages

[hex110]

Summary

• Without fakeroot, files in the .deb package are created with the build user's UID:GID instead of root:root (0:0), causing incorrect ownership when installed via dpkg
• Wraps both make install and dpkg -b with fakeroot in the client and server deb build scripts

Closes #513

[Et0h]

I'm not a Linux user, but would it be better to use dpkg-deb --root-owner-group -b instead of fakeroot here to avoid an additional build dependency?

Under this alternative, the only changes from master would be to the final package-building command in each Debian packaging script:

# ci/deb-script.sh
 make install DESTDIR=/tmp/syncplay
-dpkg -b /tmp/syncplay/
+dpkg-deb --root-owner-group -b /tmp/syncplay/

# ci/deb-server-script.sh
 make install-server DESTDIR=/tmp/syncplay-server
-dpkg -b /tmp/syncplay-server/
+dpkg-deb --root-owner-group -b /tmp/syncplay-server/

The make install / make install-server staging steps and the generated DEBIAN/prerm scripts would remain unchanged.

For clarity, this sets the ownership of filesystem entries recorded in the package to root:root (i.e. it does not cause Syncplay or the media player processes it launches to run as root).

Debian documents --root-owner-group as:

Set the owner and group for each entry in the filesystem tree data to root with id 0

It also notes that the option is useful for rootless builds: https://manpages.debian.org/trixie/dpkg/dpkg-deb.1.en.html

This directly addresses #513 by preventing the CI user’s UID/GID from being stored in the package.

The option requires dpkg 1.19.0 or newer, which should be fine for current Debian and Ubuntu CI environments. Since Syncplay does not appear to ship files that intentionally require non-root ownership, this seems cleaner and more focused than adding fakeroot.