Add named instance support matching the existing cloudflare pattern:
- credentials.sh: woodpecker-<name> loads .woodpecker.<name>.{url,token}
- credentials.sh: bare woodpecker resolves via .woodpecker.default or
WOODPECKER_INSTANCE env, with legacy flat-key fallback
- All 3 pipeline tools accept -a <instance> flag to select instance
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>