Basic nav and menus for admin app

Deliver navigation and menus for the admin app so Client Care Dashboard (and related admin areas) have clear entry points from a consistent shell.
Reuse the existing tools menu pattern—same structural approach as the main app sidebar—so admin feels familiar and engineering does not invent a second nav system.
Reuse NavUser (the control that switches company / membership via session) so admins with multiple brand memberships can change context the same way they do in tools.

The main tools experience already has a collapsible left nav in attik-frontend/src/components/navbar/Navbar.tsx: it renders favorites, items from navButtons / footButtons in attik-frontend/src/util/data/navButtons.tsx through Navlink, plus notifications and NavUser at the foot of the rail.
NavUser (attik-frontend/src/components/navbar/NavUser.tsx) shows the signed-in user; when the user has more than one membership, it exposes a “Switch Company” list that PATCHes session/{sessionToken} with selectedCompany, then reloads—so company context stays aligned with the rest of the app.
Admin is expected to live on a separate entry (e.g. admin subdomain per Admin Foundation), but auth and session should still align with tools once Better Auth / shared session work lands (ATT-1016). This ticket is the shell and nav, not the full auth migration.
Until product adds more admin destinations, the menu can start minimal (e.g. links or placeholders for Dashboard) while still matching the existing menu structure and NavUser behavior.

Frontend

Implement admin shell navigation by mirroring the existing menu structure: vertical rail, Navlink-style items (icons + labels + optional subnav), and the same permission-gating pattern used for navButtons where admin routes need it.
Reuse NavUser in the admin layout so company switching and account/session actions behave like tools (multi-company dropdown + single-membership link behavior).
Define an admin-specific nav config (parallel to navButtons) or shared primitives so Dashboard routes are first-class entries; exact route paths and subdomain layout depend on admin app routing (ATT-1015) and Decision needed for final IA.
Wire the shell into the admin app entry (folder/routing for admin) once that structure exists; tools layout today uses attik-frontend/src/app/tools/layout.tsx with Navbar—admin should follow the same component patterns without one-off markup.

Backend

No new backend surface is required for NavUser reuse if session and memberships match tools; if admin uses a different host, cookie/session behavior is covered under shared auth work, not this ticket.

attik-frontend/src/components/navbar/Navbar.tsx
attik-frontend/src/util/data/navButtons.tsx
attik-frontend/src/components/navbar/NavUser.tsx
attik-frontend/src/components/navbar/Navlink.tsx
attik-frontend/src/app/tools/layout.tsx
Related: ATT-1015 (admin shell entry), ATT-1016 (shared auth / tokens for admin)

Attik