feat: add Tekton Pipelines for integration testing

Implement Kubernetes-native CI/CD with Tekton Pipelines:

ARCHITECTURE:
- Tekton Task: Runs integration tests in container
- Tekton Pipeline: Orchestrates test execution
- ArgoCD Application: Manages Tekton installation
- CI: Triggers PipelineRun, reads results, promotes image

FLOW:
1. CI builds image:sha
2. CI creates PipelineRun with new image
3. Tekton controller watches PipelineRun
4. Task executes integration tests
5. Results written to PipelineRun status
6. CI reads status, promotes to :latest if pass
7. ArgoCD detects :latest change and deploys

BENEFITS:
✓ Kubernetes-native (CRDs, no external dependencies)
✓ DRY (parameterized Task/Pipeline)
✓ SOLID (single responsibility, clean interfaces)
✓ GitOps (Tekton managed by ArgoCD)
✓ Observable (logs, status, results)
✓ Secure (non-root, resource limits)

FILES:
- k8s/tekton/task-integration-test.yaml: Task definition
- k8s/tekton/pipeline-integration-test.yaml: Pipeline definition
- k8s/tekton/kustomization.yaml: Kustomize management
- k8s/tekton/README.md: Documentation
- k8s/argocd-apps/tekton.yaml: ArgoCD Application
- .gitea/workflows/ci.yaml: Updated CI to use Tekton

NEXT:
1. Merge PR
2. ArgoCD syncs and installs Tekton
3. First git push triggers PipelineRun
4. Integration tests run in cluster
5. Results feedback to CI

k8s/tekton/task-integration-test.yaml

@@ -0,0 +1,85 @@
+apiVersion: tekton.dev/v1
+kind: Task
+metadata:
+  name: integration-test
+  namespace: api
+  labels:
+    app: api-gateway
+    component: testing
+spec:
+  description: Run integration tests for API gateway
+  params:
+  - name: image
+    type: string
+    description: Container image to test (including tag)
+  - name: timeout
+    type: string
+    default: "5m"
+    description: Test timeout
+  results:
+  - name: result
+    description: Test result (pass/fail)
+    type: string
+  - name: message
+    description: Test summary message
+    type: string
+  steps:
+  - name: run-tests
+    image: $(params.image)
+    securityContext:
+      runAsNonRoot: true
+      runAsUser: 65532
+      allowPrivilegeEscalation: false
+    env:
+    - name: GATEWAY_URL
+      value: "http://api-gateway:8080"
+    - name: CI
+      value: "true"
+    script: |
+      #!/bin/sh
+      set -e
+      
+      echo "🧪 Starting integration tests..."
+      echo "Image: $(params.image)"
+      echo "Gateway: $GATEWAY_URL"
+      echo ""
+      
+      # Wait for gateway to be ready
+      echo "Waiting for gateway service..."
+      for i in $(seq 1 30); do
+        if curl -s $GATEWAY_URL/healthz > /dev/null 2>&1; then
+          echo "✓ Gateway is ready"
+          break
+        fi
+        echo "Attempt $i/30: Waiting for gateway..."
+        sleep 2
+      done
+      
+      # Run integration tests
+      echo "Running integration tests..."
+      if go test -v -tags=integration -timeout=$(params.timeout) ./internal/integration/...; then
+        echo "pass" | tee $(results.result.path)
+        echo "✓ All integration tests passed" | tee $(results.message.path)
+        exit 0
+      else
+        echo "fail" | tee $(results.result.path)
+        echo "✗ Some integration tests failed" | tee $(results.message.path)
+        exit 1
+      fi
+    volumeMounts:
+    - name: tmp
+      mountPath: /tmp
+    - name: home
+      mountPath: /home/nonroot
+    resources:
+      requests:
+        cpu: 250m
+        memory: 512Mi
+      limits:
+        cpu: 500m
+        memory: 1Gi
+  volumes:
+  - name: tmp
+    emptyDir: {}
+  - name: home
+    emptyDir: {}