feat: Multi-User/Admin usermanagement + Galaxy Login/Settings + Task detail improvements

- Backend: NEW AdminController with user CRUD (GET/POST/DELETE /api/v1/admin/users)
- Backend: NEW GET /api/dashboard/tasks/{id} single task endpoint
- Backend: NEW POST /api/dashboard/tasks/{id}/activity comment endpoint
- Backend: IUserRepository + UserRepository extended with GetAllAsync, DeleteAsync
- Backend: Admin DTOs (AdminUserInfo, AdminCreateUserRequest, AdminUpdateRoleRequest)
- Frontend: NEW TaskDetailView.vue — URL-based (/tasks/:id) Galaxy-themed task detail
  with subtask create/edit/delete, activity with comments, property sidebar
- Frontend: LoginView.vue — полностью Galaxy theme redesign with GalaxyBackground,
  glass-morphism card, password toggle, consistent brand
- Frontend: SettingsView.vue — Galaxy theme redesign with glass cards,
  admin user management section (create/list users, visible only to owner role)
- Frontend: TaskBoardView.vue — added "Full View" link to URL-based detail page
- Frontend: Router — added /tasks/:id route for TaskDetailView
- Frontend: App.vue — added TaskDetail to standaloneViews whitelist
- Frontend: tasks store — stable

Auth: Admin creates accounts, users log in with existing /api/v1/auth/login.
Login/Settings deliver visible Galaxy-consistent design with nexus-tokens.css tokens.

frontend/src/router.ts

@@ -12,6 +12,7 @@ import CalendarView from './views/CalendarView.vue'
 import NexusLayout from './layouts/NexusLayout.vue'
 import FlowBoard from './views/Dashboard/FlowBoard.vue'
 import TaskBoardView from './views/TaskBoardView.vue'
+import TaskDetailView from './views/TaskDetailView.vue'
 import NotificationsView from './views/NotificationsView.vue'
 
 const routes = [
@@ -36,6 +37,7 @@ const routes = [
   { path: '/projects', name: 'Projects', component: { template: '' } },
   { path: '/projects/:id', name: 'ProjectDetail', component: ProjectDetailView },
   { path: '/tasks', name: 'Task Board', component: TaskBoardView },
+  { path: '/tasks/:id', name: 'TaskDetail', component: TaskDetailView },
   { path: '/agents', name: 'Agents', component: AgentsIndexView },
   { path: '/models', name: 'Models', component: { template: '' } },
   { path: '/activity', name: 'Activity', component: { template: '' } },