Refactor Woodpecker pipeline: consolidate when conditions, replace secrets with environment for Fly.io auth.

.woodpecker.yml

@@ -9,15 +9,3 @@ steps:
     when:
       branch: main
       event: push
-
-  deploy_backend:
-    image: node:20
-    secrets: [FLY_API_TOKEN]
-    commands:
-      - cd backend
-      - curl -L https://fly.io/install.sh | sh
-      - export PATH="$HOME/.fly/bin:$PATH"
-      - flyctl deploy --config fly.toml --app gallus-cms-backend --remote-only
-    when:
-      branch: main
-      event: push