fix: revert to v2 steps format (Woodpecker 3.x still expects 'steps:' not 'pipeline:')

The linter requires 'steps:' array format with 'when:' triggers,
not the v3 'pipeline:' map format.

.woodpecker.yml

@@ -1,17 +1,17 @@
 # Woodpecker CI pipeline for DCOS
 # Integrates with stonks-ci (stonks-oracle's CI/CD at stonks-ci.celestium.life)
 
-pipeline:
-  lint-and-test:
+steps:
+  - name: lint-and-test
     image: python:3.12-slim
     commands:
       - pip install --break-system-packages ruff pytest asyncpg redis aiosqlite pyyaml
       - ruff check src/dcos/
       - pytest tests/test_memory/ tests/test_core/ -x --tb=short -q || true
-    trigger:
+    when:
       event: push
 
-  build-and-push-image:
+  - name: build-and-push-image
     image: plugins/docker
     privileged: true
     commands:
@@ -20,13 +20,13 @@ pipeline:
       - docker push ghcr.io/celesrenata/dcos:${CI_COMMIT_SHA}
       - docker tag ghcr.io/celesrenata/dcos:${CI_COMMIT_SHA} ghcr.io/celesrenata/dcos:latest
       - docker push ghcr.io/celesrenata/dcos:latest
-    trigger:
+    when:
       event: push
 
-  deploy-to-k8s:
+  - name: deploy-to-k8s
     image: bitnami/kubectl:latest
     commands:
       # Deploy using runmefirst.sh (handles secrets, namespace, GHCR pull secret)
       - bash ~/sources/kube/dcos/runmefirst.sh
-    trigger:
+    when:
       event: push