k8s-portal: build off-infra GHA -> ghcr + Keel; remove Woodpecker build (no-local-builds)

The last in-cluster image build. GHA build-k8s-portal.yml builds
ghcr.io/viktorbarzin/k8s-portal:latest+sha (path-filtered on the Dockerfile
dir); Keel (force/poll/match-tag) rolls the deployment. Stack image repointed
to ghcr (ignore_changed); .woodpecker/k8s-portal.yml deleted.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.woodpecker/k8s-portal.yml

@@ -1,49 +0,0 @@
-when:
-  event: push
-  branch: master
-  path:
-    include:
-      - "stacks/platform/modules/k8s-portal/files/**"
-
-clone:
-  git:
-    image: woodpeckerci/plugin-git
-    settings:
-      attempts: 5
-      backoff: 10s
-
-steps:
-  - name: build-and-push
-    image: woodpeckerci/plugin-docker-buildx
-    settings:
-      username: "viktorbarzin"
-      password:
-        from_secret: dockerhub-pat
-      repo: viktorbarzin/k8s-portal
-      dockerfile: stacks/platform/modules/k8s-portal/files/Dockerfile
-      context: stacks/platform/modules/k8s-portal/files
-      platforms:
-        - linux/amd64
-      tag: ["${CI_PIPELINE_NUMBER}", "latest"]
-      cache_from: "viktorbarzin/k8s-portal:latest"
-      cache_to: "type=inline"
-
-  - name: deploy
-    image: bitnami/kubectl:latest
-    commands:
-      - "kubectl set image deployment/k8s-portal portal=viktorbarzin/k8s-portal:${CI_PIPELINE_NUMBER} -n k8s-portal"
-      - "kubectl rollout status deployment/k8s-portal -n k8s-portal --timeout=120s"
-      - "echo 'k8s-portal deployed successfully (build ${CI_PIPELINE_NUMBER})'"
-
-  - name: slack
-    image: curlimages/curl
-    commands:
-      - |
-        curl -s -X POST -H 'Content-type: application/json' \
-          --data "{\"text\":\"K8s Portal: build #${CI_PIPELINE_NUMBER} ${CI_PIPELINE_STATUS}\"}" \
-          "$SLACK_WEBHOOK" || true
-    environment:
-      SLACK_WEBHOOK:
-        from_secret: slack_webhook
-    when:
-      status: [success, failure]