feat(backend): Implement Day 6 Role Management API

Add complete role management functionality for tenant administrators to manage user roles within their tenants.

Changes:
- Extended IUserTenantRoleRepository with pagination, role counting, and last owner check methods
- Extended IUserRepository with GetByIdAsync(Guid) and GetByIdsAsync for flexible user retrieval
- Extended IRefreshTokenRepository with GetByUserAndTenantAsync and UpdateRangeAsync
- Implemented repository methods in Infrastructure layer
- Created DTOs: UserWithRoleDto and PagedResultDto<T>
- Implemented ListTenantUsersQuery with pagination support
- Implemented AssignUserRoleCommand to assign/update user roles
- Implemented RemoveUserFromTenantCommand with token revocation
- Created TenantUsersController with 4 endpoints (list, assign, remove, get-roles)
- Added comprehensive PowerShell test script

Security Features:
- Only TenantOwner can assign/update/remove roles
- Prevents removal of last TenantOwner (lockout protection)
- Prevents manual assignment of AIAgent role (reserved for MCP)
- Cross-tenant access protection
- Automatic refresh token revocation when user removed

API Endpoints:
- GET /api/tenants/{id}/users - List users with roles (paginated)
- POST /api/tenants/{id}/users/{userId}/role - Assign/update role
- DELETE /api/tenants/{id}/users/{userId} - Remove user from tenant
- GET /api/tenants/roles - Get available roles

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

colaflow-api/src/Modules/Identity/ColaFlow.Modules.Identity.Application/Queries/ListTenantUsers/ListTenantUsersQuery.cs

@@ -0,0 +1,10 @@
+using ColaFlow.Modules.Identity.Application.Dtos;
+using MediatR;
+
+namespace ColaFlow.Modules.Identity.Application.Queries.ListTenantUsers;
+
+public record ListTenantUsersQuery(
+    Guid TenantId,
+    int PageNumber = 1,
+    int PageSize = 20,
+    string? SearchTerm = null) : IRequest<PagedResultDto<UserWithRoleDto>>;

colaflow-api/src/Modules/Identity/ColaFlow.Modules.Identity.Application/Queries/ListTenantUsers/ListTenantUsersQueryHandler.cs

@@ -0,0 +1,58 @@
+using ColaFlow.Modules.Identity.Application.Dtos;
+using ColaFlow.Modules.Identity.Domain.Repositories;
+using MediatR;
+
+namespace ColaFlow.Modules.Identity.Application.Queries.ListTenantUsers;
+
+public class ListTenantUsersQueryHandler : IRequestHandler<ListTenantUsersQuery, PagedResultDto<UserWithRoleDto>>
+{
+    private readonly IUserTenantRoleRepository _userTenantRoleRepository;
+    private readonly IUserRepository _userRepository;
+
+    public ListTenantUsersQueryHandler(
+        IUserTenantRoleRepository userTenantRoleRepository,
+        IUserRepository userRepository)
+    {
+        _userTenantRoleRepository = userTenantRoleRepository;
+        _userRepository = userRepository;
+    }
+
+    public async Task<PagedResultDto<UserWithRoleDto>> Handle(
+        ListTenantUsersQuery request,
+        CancellationToken cancellationToken)
+    {
+        var (roles, totalCount) = await _userTenantRoleRepository.GetTenantUsersWithRolesAsync(
+            request.TenantId,
+            request.PageNumber,
+            request.PageSize,
+            request.SearchTerm,
+            cancellationToken);
+
+        var userDtos = new List<UserWithRoleDto>();
+
+        foreach (var role in roles)
+        {
+            var user = await _userRepository.GetByIdAsync(role.UserId, cancellationToken);
+
+            if (user != null)
+            {
+                userDtos.Add(new UserWithRoleDto(
+                    user.Id,
+                    user.Email.Value,
+                    user.FullName.Value,
+                    role.Role.ToString(),
+                    role.AssignedAt,
+                    user.EmailVerifiedAt.HasValue));
+            }
+        }
+
+        var totalPages = (int)Math.Ceiling(totalCount / (double)request.PageSize);
+
+        return new PagedResultDto<UserWithRoleDto>(
+            userDtos,
+            totalCount,
+            request.PageNumber,
+            request.PageSize,
+            totalPages);
+    }
+}