feat(sidebar): integrate NavUser component into SidebarFooter and clean up SiteHeader

- Added NavUser component to the SidebarFooter for user information display.
- Refactored SiteHeader by removing unused imports and components related to user account management.
- Updated breadcrumbs logic to include a new path for admin apps.
- Adjusted SidebarMenuItem formatting for improved readability.

docs/ui-design-contract.md

@@ -16,7 +16,8 @@ Surface lock: **`frame`** (ReUI Frame). Не смешивать shadcn Card и F
 | Sidebar / hover colors | theme `--sidebar` / `--sidebar-accent` — **без** AppShell `color-mix` override |
 | Header | `h-12`, `sticky`, `border-b`, `px-4 md:px-6` |
 | Header left | `SidebarTrigger` + `Separator` + Breadcrumb |
-| Header right | **AppsMenu** → **ModeToggle** (+ account menu; SystemMonitor — stub/нет) |
+| Header right | **AppsMenu** (аккаунт — в sidebar footer `NavUser`) |
+| Sidebar footer | **NavUser** — аватар, имя, email, тема, выход · [app-shell-12](https://reui.io/preview/base/app-shell-12) |
 | Sidebar | AppSwitcher → groups → icons `size-4` → **пустой** `SidebarFooter` |
 | `main` | `gap-4 md:gap-6`, `px-4 py-4 md:px-6 md:py-5` |