feat: add Tekton Pipelines for integration testing (#25)

Implement Kubernetes-native CI/CD with Tekton Pipelines for pre-merge integration testing.

## What This Does

Adds Tekton Pipelines to orchestrate integration tests before deployment:

1. **Tekton Task** (task-integration-test.yaml)
   - Runs integration tests in container
   - Tests memory, S3, SQS, workflow, IAM services
   - Reports pass/fail results

2. **Tekton Pipeline** (pipeline-integration-test.yaml)
   - Parameterized pipeline for reusability
   - Takes image tag as input
   - Outputs test results

3. **ArgoCD Application** (k8s/argocd-apps/tekton.yaml)
   - Manages Tekton installation
   - Tekton controller watches and executes PipelineRuns
   - No manual kubectl applies needed

4. **Updated CI** (.gitea/workflows/ci.yaml)
   - Build image with commit SHA
   - Create PipelineRun to test image
   - Wait for Tekton to complete tests
   - Only promote to :latest if tests pass
   - ArgoCD detects :latest and deploys

## Architecture

git push → CI builds image:sha → Create PipelineRun → Tekton runs tests → Results to CI → Promote :latest → ArgoCD deploys

## Code Quality

✓ DRY: Parameterized, reusable Task and Pipeline
✓ SOLID: Single responsibility, clean interfaces
✓ GitOps: Everything in git, managed by ArgoCD
✓ Security: Non-root containers, resource limits
✓ Observable: Logs, status, results tracking

## Files Changed

- k8s/tekton/task-integration-test.yaml - Task definition
- k8s/tekton/pipeline-integration-test.yaml - Pipeline definition
- k8s/tekton/kustomization.yaml - Kustomize for management
- k8s/tekton/base/tekton-release.yaml - Release reference
- k8s/tekton/README.md - Documentation
- k8s/argocd-apps/tekton.yaml - ArgoCD Application
- .gitea/workflows/ci.yaml - Updated CI workflow

## Review Checklist

- [ ] Tekton manifests are clean and parameterized
- [ ] ArgoCD Application properly configured
- [ ] CI workflow correctly triggers PipelineRun
- [ ] Error handling for test failures
- [ ] Logs and status properly captured
- [ ] Documentation is clear

## Testing

After merge:
1. ArgoCD syncs and installs Tekton Pipelines
2. Next git push triggers CI
3. CI creates PipelineRun
4. Tekton runs integration tests
5. Results show in CI workflow

---------

Co-authored-by: poimen <[email protected]>
Reviewed-on: #25
Co-authored-by: poimen <[email protected]>

internal/integration/integration_test.go

@@ -247,7 +247,7 @@ func TestIntegrationIAMService(t *testing.T) {
 	}
 	defer resp.Body.Close()
 
-	body, _ := io.ReadAll(resp.Body)
+	_, _ = io.ReadAll(resp.Body)
 	t.Logf("IAM list users response: %d", resp.StatusCode)
 
 	// IAM (Authentik) should respond - 200, 404, or auth error all prove routing works