Marking your own outgoing mail as spam makes no sense, but the action
was offered in every non-junk folder: context menu, hover quick-actions,
viewer toolbar and its overflow menu, plus the "!" shortcut.
All surfaces now skip the action when the folder role is sent, drafts or
scheduled, and the shortcut is a no-op there. Scheduled messages were
already covered per-email via isScheduled; the role check additionally
covers the server-side Scheduled folder before that annotation loads.
The hover quick-actions bar gets a spamApplicable prop for this, since
it renders its buttons without knowing the folder.
