feat: put Star and Archive on the message bar too

Follows items 185 and 186, which established the pane's bar as where actions
on the displayed message live. Star and Archive are both selection-scoped and
fit that rule with nothing to decide; Archive leaves the main toolbar the way
Delete did, since the same icon in two places reads as two controls when the
toolbar is icon-only.

Ordered by what they do rather than by where they came from: answering the
message, then filing it, then destroying it, so the destructive button is not
between two that are not.

Mark all read deliberately stays on the main toolbar, at the user's decision.
It is the one action in this window that ignores the selection and acts on
every row in the view, so a bar whose every other entry acts on the one
displayed message is exactly where it must not be.

Item 140's toolbar test named archive as an example of a list-wide action.
That was never true of it, only untested, and this item reclassifies it: the
test now asserts archive LEFT the toolbar and keeps its guard on
mark_all_read, which is the action that genuinely is list-wide.

Closes item 189.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NY6poqw199LfFaXe5BHKNe

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