rune v0.5.4

Multi-agent interoperability.

- AGENTS.md generated on sync with XML skill metadata (agentskills.io format).
  Parsed by Cursor, Windsurf, Copilot, Aider, and other agent editors.
- .agent/skills/ symlink to .claude/skills/ for non-Claude agent discovery.
- Fix: push new directory-style skills to registry correctly.
- Pipeline component v2.3.0.