feat(install): add --force to repoint symlinks; document worktree caveat

install.sh skipped a symlink pointing at another checkout, so there was
no scripted way to take the live set over. Add a --force flag that
repoints such divergent symlinks at the invoking clone (default run still
skips, stays idempotent). Document in INSTALL.md that the plugin must be
developed in the primary clone, not a worktree, and that --force repoints.

closes #17

INSTALL.md

@@ -60,4 +60,14 @@ cd ~/dev/skills && git pull
 Symlinks pick up the changes automatically. If new skills or
 agents have been added, re-run `install.sh` to add the new
 symlinks (it is idempotent and will not overwrite existing
-ones).
+ones — pass `--force` to repoint a symlink that points at a
+different checkout).
+
+## Worktrees
+
+The symlinks target the absolute path of the clone `install.sh` was
+run from. Develop this plugin only in that primary clone, never from a
+git worktree: a running session loads skills, agents, and workflows
+through the symlinks regardless of cwd, so worktree edits are not what
+it executes (see `CLAUDE.md`). To take the live set over from a
+different checkout, run `./install.sh --force` from it.