Give both kinds of card the same anatomy

A question the room answered and a comment the room accepted are the same kind
of thing, and looked nothing alike: one had a header and no provenance, the
other provenance and no header. Two components drawing similar chrome by
convention is how that happens, so the chrome moved into a shell both use, and
neither draws its own any more. The header names the kind; the footer's verb
carries the status, because "accepted by" and "answered by" already say it.

The footer was not just missing for questionnaires, it was impossible.
QuestionView has rendered "Answered by @x" all along and nothing could pass it
a resolver: the client builds those cards from the document, and the document
recorded no such thing. There was no timestamp anywhere either, not even in the
server's record.

So a questionnaire now records who settled it and when, in the plan, the way an
accepted comment already did. On the container rather than on each answer,
because it resolves as a unit — derive is all-or-nothing — so every Answer
would otherwise repeat one handle and one moment. Decision carries its
provenance the same way, which makes the two identical in shape rather than
merely similar. That took a deviation from what was agreed, which said Answer;
the reasoning is in the dialect.

Both attributes are optional, so every existing plan.mdx still validates, and
no wire change was needed: the client already reads the whole questionnaire off
the node.

One questionnaire answered before any of this will show no footer. Its record
has a resolver but the file has nothing and there is no timestamp to recover.
Not backfilled on load — the plan is a file a person can edit between runs, and
correcting it at startup is the thing we decided against for missing Decision
nodes.

The shell insets its own body except where the body already insets itself,
which QuestionView does and cannot stop doing from another package.