fix(composer): badge a slash word only when it is a real command - #727

A bare `/word` became a command badge on shape alone. The composer fills
itself from text in several places -- a paste, a restored draft, a quick
message, a reopened queued message, a to-do brief -- and every one of them
ran the same heuristic: start of line or after a space, `/` or `$`, a
letter, no trailing slash. `/notacommand`, `/etc`, `/nope` all passed, and
the user had picked none of them from the menu. What came back was an
atomic node: the word could no longer be edited in place, its `/` was gone
from the label, and its text was rebuilt on send from the badge's id rather
than kept -- which for an id the serializer has to escape (`/foo_`) is not
even the same bytes.

A badge now requires the token to be one the agent advertises right now,
matched exactly: the tokens behind the `/` and `$` menus themselves, so
what seeded text may become is precisely what the menu could have inserted.
`/rev` is not `/review`, `/Review` is not `/review` (the CLI reads the name
it advertised), and with no list yet -- the connection still coming up, or
no agent behind the box at all -- nothing is badged. That direction is the
safe one: text that stays text is still editable and still sends verbatim.

Picking from the menu is untouched, trailing space included, as are badges
already in the document; a list that lands mid-compose applies to the next
paste and rewrites nothing already written. Reference links keep hydrating
regardless -- a `file:`/`codeg:` destination was inserted deliberately and
says so. The transcript keeps the heuristic on its own: a sent message is
fixed text, and gating it on a list that comes and goes with the connection
would re-badge history underneath the reader.