Sentinel Linux public branding transition 1.0.2

This package changes visible distribution-name and boot/login artwork only:
- public release name and issue text;
- GRUB distributor and package-owned Sentinel Linux theme;
- corrected GRUB title positioning using a supported label component;
- LightDM background override;
- static Sentinel Linux Plymouth splash and wordmark.

Legacy package names, commands, filesystem paths, GTK/icon/cursor identifiers,
policy rules, security settings, application versions and ID=sentinelos remain
unchanged for compatibility.
