Agent Skills: woodpecker-pipelines

Patterns and hard-won gotchas for designing, debugging, and writing Woodpecker CI pipeline files. Use when authoring or editing `.woodpecker.yml` / `.woodpecker/*.yml`, when a pipeline shows `error` status with no step logs, when shell variables in `commands:` blocks are not interpolating as expected, when splitting between single-file and multi-pipeline directory layouts, or when running iOS signing / archive flows on a non-interactive Mac agent. Companion to the `woodpecker-cli` skill (which is the CLI reference) — this one is the workflow-design + debugging reference.