fix: export COLUMNS LINES before exec sbcl

bash sets COLUMNS and LINES but doesn't export them to
subprocesses. Without export, SBCL's posix-getenv returns nil
and the terminal size fallback fails. Add explicit export
before the exec sbcl line.

passepartout

@@ -406,6 +406,9 @@ case "$COMMAND" in
   (sleep 3) (finish-output) (uiop:quit 1))))
   (passepartout.channel-tui:tui-main))
 LISPEOF
+        # Export terminal dimensions — bash sets COLUMNS/LINES but
+        # doesn't export them to subprocesses by default.
+        export COLUMNS LINES
         exec sbcl --noinform --load /tmp/tui-load.lisp
         ;;
     gateway)