Add <Decision> and <Note> to the plan dialect

An accepted comment thread is projected into the plan so the source carries
the decision when read alone. Atomic like a questionnaire: the record beside
the plan owns the thread, and an accepted one is frozen, so there is nothing
inside for two people to edit.

A note's text is an attribute rather than children, following <Answer>. A flow
component's children parse as blocks, so prose written between the tags comes
back wrapped in a paragraph and flattens on the way out — which the plan's
round-trip check rejects the whole document for. Attributes round-trip
newlines, quotes and angle brackets exactly, and the quote delimiter is
escaped, so a note cannot break out into a second component.

Renders as nothing inline: the card belongs in the sidecar.