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.

backend/Controllers/DashboardController.cs

@@ -3,6 +3,7 @@ using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 using Nexus.Api.Data;
 using Nexus.Api.Models;
+using Nexus.Api.Repositories;
 using Nexus.Api.Services;
 
 namespace Nexus.Api.Controllers;
@@ -13,6 +14,7 @@ namespace Nexus.Api.Controllers;
 public class DashboardController(
     IDashboardService dashboardService,
     ITaskService taskService,
+    IActivityRepository activityService,
     IHttpContextAccessor httpContextAccessor) : ControllerBase
 {
     [HttpGet("status")]
@@ -239,6 +241,14 @@ public class DashboardController(
         return Ok(children.Select(MapToDto).ToList());
     }
 
+    [HttpGet("tasks/{id:guid}")]
+    public async Task<ActionResult<DashboardTaskDto>> GetTask(Guid id, CancellationToken ct)
+    {
+        var task = await taskService.GetByIdAsync(id, ct);
+        if (task is null) return NotFound(new { error = "Task not found." });
+        return Ok(MapToDto(task));
+    }
+
     [HttpGet("tasks/{id:guid}/activity")]
     public async Task<ActionResult<List<ActivityEvent>>> GetTaskActivity(Guid id, CancellationToken ct)
     {
@@ -246,14 +256,25 @@ public class DashboardController(
         return Ok(events);
     }
 
-    // ── Import ──
-
-    [HttpPost("tasks/import-from-iris-todo")]
-    public async Task<ActionResult<ImportResultDto>> ImportFromIrisTodo(
-        [FromQuery] bool delete = false, CancellationToken ct = default)
+    [HttpPost("tasks/{id:guid}/activity")]
+    public async Task<ActionResult<ActivityEvent>> PostTaskActivity(
+        Guid id, [FromBody] PostActivityRequest request, CancellationToken ct)
     {
-        var result = await taskService.ImportFromIrisTodoAsync(delete, ct);
-        return Ok(new ImportResultDto(result));
+        var task = await taskService.GetByIdAsync(id, ct);
+        if (task is null) return NotFound(new { error = "Task not found." });
+
+        if (string.IsNullOrWhiteSpace(request.Message))
+            return BadRequest(new { error = "Message is required." });
+
+        var ev = new ActivityEvent
+        {
+            Type = request.Type ?? "comment",
+            Message = request.Message.Trim(),
+            TaskId = id
+        };
+
+        await activityService.AddAsync(ev, ct);
+        return Created($"/api/dashboard/tasks/{id}/activity/{ev.Id}", ev);
     }
 
     private static DashboardTaskDto MapToDto(WorkTask t) => new(