I can't seem to find any extension/module/etc that does this nicely.
You can access the column metadata as follows, but I want a good way to display it as a flowchart or hypergraph in a model's index.
$m=new MyModel;
Yii::log(CVarDumper::dumpAsString($m->tableSchema->columns),'warning');
// echo $m->toJSON(); // uses json behavior, will give this to a js flowchart to show the schema