docs: settle item 187 on Trash's shapeHEADmaster

Three decisions from the user. Spam is path-based like Trash, not a tag
generator: a tag query finds only what this application marked and misses
everything the server filed, which is most of what those folders hold. Mark
spam moves the file, as Delete does, which is what makes a path-based view
honest and is a change to an existing action rather than only a new view. The
Junk folder one account carries is out of scope.

Every account can reach a spam folder now. The three channels that listed
their folders explicitly gained the provider's spam folder this session,
verified against mbsync --list rather than guessed, since Create Both turns a
wrong name into a folder created on the server.

Records the cleanup pass as a copy of showStrandedDeletedMail() from item 103,
which solves the same problem one version earlier: it reports mail whose file
never moved and leaves the user to act, and its empty-list and AlreadyScoped
details are load-bearing. Notes that a mandatory spam key breaks existing
configs on upgrade exactly as trash did, and that the trash predicate behind
the message bar must not treat a spam folder as a trash one.

Resized S to M: the move path, the origin tag and the cleanup are three parts.

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

0 files changed, 0 insertions, 0 deletions