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/README.md

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+# Tekton Integration Testing
+
+Tekton Pipelines for running integration tests on API Gateway changes before merging to main.
+
+## Architecture
+
+```
+Gitea CI (builds image:sha)
+    ↓
+Creates PipelineRun
+    ↓
+Tekton Controller (watches PipelineRun)
+    ↓
+Runs Task: integration-test
+    ↓
+Task runs tests in container
+    ↓
+Reports pass/fail to PipelineRun status
+    ↓
+CI reads status and promotes image (if pass)
+    ↓
+ArgoCD deploys new image
+```
+
+## Components
+
+### Task: `integration-test`
+- **File**: `task-integration-test.yaml`
+- **Purpose**: Run integration tests in a container
+- **Inputs**: Image to test, timeout
+- **Outputs**: pass/fail result, message
+- **Security**: Non-root user, resource limits
+
+### Pipeline: `integration-test-pipeline`
+- **File**: `pipeline-integration-test.yaml`
+- **Purpose**: Orchestrate integration test execution
+- **Tasks**: Runs the integration-test task
+- **Results**: Aggregates task results for CI consumption
+
+## Usage
+
+### Manual Trigger
+
+```bash
+# Create a PipelineRun to test an image
+kubectl create -f - << 'YAML'
+apiVersion: tekton.dev/v1
+kind: PipelineRun
+metadata:
+  name: integration-test-manual
+  namespace: api
+spec:
+  pipelineRef:
+    name: integration-test-pipeline
+  params:
+  - name: image
+    value: forgejo.riotpiao.com/rock/api-gateway:abc123
+  - name: test-timeout
+    value: "5m"
+YAML
+
+# Watch test progress
+kubectl logs -f -n api pipelinerun/integration-test-manual
+
+# Check results
+kubectl get pipelinerun -n api integration-test-manual -o yaml
+```
+
+### CI Trigger
+
+CI automatically creates PipelineRun with:
+- Image tag: current commit SHA
+- Timeout: 5 minutes
+- Labels: PR ID, commit SHA for traceability
+
+## Management
+
+Tekton is managed by ArgoCD Application: `tekton-pipelines` (in `k8s/argocd-apps/tekton.yaml`)
+
+To update:
+1. Edit manifest files
+2. Commit to git
+3. ArgoCD syncs automatically
+
+Do NOT manually apply manifests - let ArgoCD manage everything.
+
+## Monitoring
+
+```bash
+# List all PipelineRuns
+kubectl get pipelineruns -n api
+
+# Watch a specific run
+kubectl logs -f -n api pipelinerun/integration-test-<sha>
+
+# Get detailed status
+kubectl describe pipelinerun -n api integration-test-<sha>
+```
+
+## Results
+
+PipelineRun status contains:
+- `status.conditions[0].reason`: Succeeded | Failed | Unknown
+- `status.taskRuns[*].status.taskResults`: Test outputs
+- Pod logs: Detailed test output
+
+## Best Practices
+
+1. **DRY**: Task and Pipeline are parameterized, reusable
+2. **SOLID**: Single responsibility (Task runs tests, Pipeline orchestrates)
+3. **GitOps**: Everything in git, managed by ArgoCD
+4. **Security**: Non-root containers, resource limits, no hardcoded values
+5. **Observability**: Clear logging, status tracking, result aggregation
+
+## Troubleshooting
+
+**PipelineRun stuck in Running**
+- Check pod logs: `kubectl logs -n api pod/<task-pod>`
+- Check gateway availability: `kubectl get pods -n api -l app=api-gateway`
+- Increase timeout in pipeline params
+
+**Tests failing**
+- Check test logs: `kubectl logs -n api pipelinerun/<run-name>`
+- Verify gateway is ready and accessible
+- Check downstream services (memory, S3, etc.)
+
+**Image not promoted**
+- CI only promotes if PipelineRun succeeds
+- Check PipelineRun status: `kubectl get pipelinerun <name> -n api -o yaml`
+- Review CI logs in Gitea for error details

k8s/tekton/base/tekton-release.yaml

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+# Tekton Pipelines Release manifest
+# Source: https://storage.googleapis.com/tekton-releases/pipeline/latest/release.yaml
+# This is managed by ArgoCD - do NOT manually apply
+# ArgoCD syncs this from git
+
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: tekton-pipelines
+  labels:
+    managed-by: argocd
+
+---
+# CRDs and RBAC are part of the full release manifest
+# Using a reference approach for cleaner GitOps
+apiVersion: argoproj.io/v1alpha1
+kind: ApplicationSet
+metadata:
+  name: tekton-pipelines
+  namespace: argocd
+spec:
+  generators:
+  - list:
+      elements:
+      - name: tekton-pipelines
+  template:
+    metadata:
+      name: tekton-pipelines
+      namespace: argocd
+    spec:
+      project: default
+      source:
+        repoURL: https://github.com/tektoncd/operator
+        targetRevision: main
+        path: config/release
+      destination:
+        server: https://kubernetes.default.svc
+        namespace: tekton-pipelines
+      syncPolicy:
+        automated:
+          prune: true
+          selfHeal: true
+        syncOptions:
+        - CreateNamespace=true

k8s/tekton/kustomization.yaml

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+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+metadata:
+  name: api-gateway-tekton
+
+namespace: api
+
+resources:
+- task-integration-test.yaml
+- pipeline-integration-test.yaml
+
+commonLabels:
+  app: api-gateway
+  component: testing
+  managed-by: argocd

k8s/tekton/pipeline-integration-test.yaml

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+apiVersion: tekton.dev/v1
+kind: Pipeline
+metadata:
+  name: integration-test-pipeline
+  namespace: api
+  labels:
+    app: api-gateway
+    component: testing
+spec:
+  description: Pipeline to run integration tests for API gateway
+  params:
+  - name: image
+    type: string
+    description: Container image to test (repo:tag)
+    default: "forgejo.riotpiao.com/rock/api-gateway:latest"
+  - name: test-timeout
+    type: string
+    default: "5m"
+    description: Test execution timeout
+  results:
+  - name: test-result
+    description: Overall test result (pass/fail)
+    value: $(tasks.run-integration-tests.results.result)
+  - name: test-message
+    description: Test summary message
+    value: $(tasks.run-integration-tests.results.message)
+  tasks:
+  - name: run-integration-tests
+    taskRef:
+      name: integration-test
+    params:
+    - name: image
+      value: $(params.image)
+    - name: timeout
+      value: $(params.test-timeout)

k8s/tekton/task-integration-test.yaml

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+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: {}