feat(hyprland): add minimal waybar clock baseline and ADR

[rrvsh]

Summary

• enable Waybar in the Hyprland Home Manager module with an intentionally minimal bar layout
• render only a right-aligned clock with Weekday, DD/MM/YYYY HH:MM:SS and transparent styling with white text
• add an ADR and session notes documenting the NixOS/Hyprland-scoped architecture and implementation direction