feat(saas): implement marketplace and tenant onboarding

Tiku.Api/Controllers/TenantOnboardingController.cs

@@ -0,0 +1,25 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using Tiku.Application.Security;
+using Tiku.Application.Tenancy;
+
+namespace Tiku.Api.Controllers;
+
+[ApiController]
+[Route("api/tenant-onboarding")]
+[Authorize(Policy = BackendPermissions.TenantSettingsManage)]
+public sealed class TenantOnboardingController(
+    ITenantOnboardingService onboardingService,
+    ICurrentAccessContext accessContext) : ControllerBase
+{
+    [HttpGet("status")]
+    public async Task<TenantOnboardingStatus> Status(CancellationToken cancellationToken)
+    {
+        var access = await accessContext.GetAsync(cancellationToken);
+        if (access.TenantId is not { } tenantId || !access.IsCurrentTenantMember)
+        {
+            throw new TenantExternalProviderException("Tenant onboarding access is denied.", "tenant_access_denied");
+        }
+        return await onboardingService.GetStatusAsync(tenantId, cancellationToken);
+    }
+}