NexusOS v3.1.0 - Admin UI Finalization

Fresh install package.

Included:
- Finalized admin shell layout.
- Fixed sidebar/content alignment standards.
- Stable light/dark mode contrast palette.
- Unified card/table/form/button design.
- Finalized Roles & Permissions visual structure.
- Finalized Theme Control, Cache, Log, Queue and Profile screen standards.
- Responsive admin layout improvements.
