Update agent instructions; check a worktree is clean before its pre-rm hook

- AGENTS.md and the skill: only the user's browser is off (xdg-open); browser tools run
  in the sandbox, headless or in a Wayland window; host-run project files are read-only
- wt rm: refuse a dirty worktree before wt-pre-rm runs, so its stack is not stopped for
  nothing

lib/worktree.sh

@@ -64,12 +64,12 @@ ocsb_wt_rm() {
   [[ $(realpath "${dir}") != "$(realpath "${main}")" ]] || ocsb_die "refusing to remove the main worktree"
   branch=$(git -C "${dir}" rev-parse --abbrev-ref HEAD 2>/dev/null || true)
   export WT_DIR=${dir} WT_BRANCH=${branch} WT_SLUG=${name##*/} MAIN_ROOT=${main}
-  ocsb_wt_hook wt-pre-rm "${dir}" "${extra[@]}"
   status=$(git -C "${dir}" status --porcelain)
   if [[ -n ${status} && ${force} -ne 1 ]]; then
     echo "${status}" >&2
     ocsb_die "worktree has uncommitted changes — commit them or pass --force (they will be lost)"
   fi
+  ocsb_wt_hook wt-pre-rm "${dir}" "${extra[@]}"
   if [[ ${force} -eq 1 ]]; then
     git -C "${main}" worktree remove --force "${dir}"
   else