Agents can anchor a spec to code
- New MCP tool add_code_ref: an agent attaches GitHub permalinks with a note and a kind, in one batch, and each ref reports whether it was added, rejected or already there.
- get_spec now returns the refs already on a spec, so an agent stops re-proposing the same ones.
- A new spec defaults to its creator as owner. An unowned spec has nobody to chase.