Table-size quad

Before 3d calibration, it was really nice to be able to draw things in table space, regions that were rectilinear to the table.

We should have some nouns/verbs around drawing to the table. We should support real-world units for the drawing.

This might be supported by defining a table-wide region with tag pairs.

No files, tests, or entry points are named. Start by locating the existing drawing, table-space, and tag-pair handling, then clarify the nouns, verbs, and real-world-unit behavior; done means table-space drawing supports the agreed rectilinear regions and units.

Written by the indexing model from the issue text.