fix: worktree created in wrong directory (issue #185)

cmd_start was calling create_worktree without passing $WORKTREES_DIR,
causing worktrees to be created in $PWD (daemon's working directory)
instead of ~/.kugetsu-worktrees/

skills/kugetsu/scripts/kugetsu-session.sh

@@ -246,7 +246,7 @@ cmd_start() {
     local before_sessions=$(opencode session list 2>/dev/null | grep -oP '^ses_\w+' | sort)
     local before_set="|$before_sessions|"
     
-    create_worktree "$issue_ref"
+    create_worktree "$issue_ref" "$WORKTREES_DIR"
     
     local after_sessions=$(opencode session list 2>/dev/null | grep -oP '^ses_\w+' | sort)
     local new_session_id=""