A session now claims a ticket by assigning it to the dev driving the
map, rather than setting a `wayfinder:claimed` label. The assignee is
the claim; an open, unassigned ticket is unclaimed. Reads more naturally
in the tracker's own UI and frees the label vocabulary to
`wayfinder:<type>` alone.
Updates the GitHub and GitLab tracker-operations docs to the assignee
mechanism (`--add-assignee @me` / `--assignee @me`). The local-markdown
tracker keeps its `Status: claimed` line — a file store has no assignee.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
