README: replace the single-deft.so install instructions with the per-feature
plugin table (palette, switch, radial, acme, sam, plumb), a glob install loop,
and a note that the plugins cooperate by resolving each other's actions by
object name; refresh the layout tree (plugin/ gone, switch/ added, palette/ and
radial/ now hold their plugins) and mark milestones 5 and 6 DONE.
PLAN.md: add an architecture note at the top flagging the split and that the
design prose below refers to the former monolith as historical.
ed3bd4249b