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/argocd-apps/tekton.yaml

@@ -0,0 +1,33 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: tekton-pipelines
+  namespace: argocd
+  labels:
+    app.kubernetes.io/name: tekton
+    app.kubernetes.io/part-of: homelab
+spec:
+  project: default
+  
+  source:
+    repoURL: https://github.com/tektoncd/operator.git
+    targetRevision: main
+    path: config/release
+  
+  destination:
+    server: https://kubernetes.default.svc
+    namespace: tekton-pipelines
+  
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true
+    syncOptions:
+    - CreateNamespace=true
+    - Validate=false
+    retry:
+      limit: 5
+      backoff:
+        duration: 5s
+        factor: 2
+        maxDuration: 3m