Gate releases on doc status

Front matter is data. mdsmith lets a release script query it.

mdsmith list query 'status: "✅"' plan/ selects files by a CUE expression on front matter. It prints the matching paths, so a script can block a release while any plan is unfinished.

mdsmith metrics rank --by token-estimate --top 10 docs/ ranks files by any shared metric. Both commands emit plain lines, ready to pipe into the rest of a pipeline.

See the list query and metrics references for the full expression grammar and metric list.