pprint: Fix crash with `group`/`cover`/etc. due to bad code

Now we define "subject-deisired" preference; and explicitly rank stuff
during flatten.

d7, soma: implement better cursor subsume under `Rhodium`

- Smart subsumption is now completely under `Rhodium`, split into two
steps: one is cursorstep which collects info about cursors in the doc,
and another when the edit event is handled. The info is stored under
`#cursors` shadow attribute in the doc.
- Document now supports only one active `@user` cursor. It is chosen
with care, so that we do not trigger copies of it in e.g. log nodes,
cells, or fragments. `@user` cursor has a "reputation" now, incremented
when it is interacted with by the user successfully.
- `cursordepth` that we use all over the place now has an overload that
supports `#cursors`. Use it in nodestep etc. Use it soma and in other
places for consistent cursor tracking.

With this change much more reflection becomes controlled. We now don't
necessarily need to be afraid of e.g. cursors arriving via sensors and
doing something nasty at receipt; since now the original cursor in the
document will have a higher reputation and the one that arrived will not
receive anything (due to one-`@user` cursor rule).

Cursors that are not `@user` can still be created in any amounts; we do
not apply the "smart" stuff to them. They just work, anywhere and
everywhere, like all cursors behaved before this commit.

readme: Upload new soma6 demo video

uiR: fix typo

mgmt, soma: add support for `SOMA_RESOURCES_DIR` env dir, query max a…

…ntialiasing level