Move a rule several places in one change

The Rules page has a Move… button that puts a rule before any other of
its chain, or at the end, in one move. Staged in a changeset, a move
right after a move of the same object takes its place, so pressing ↑
three times is one operation; moving it back where it was takes the
operation out.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/design.md

@@ -56,7 +56,10 @@ As in Jarl, a change can be made at once or staged in a **changeset**,
 to be reviewed and applied together with others:
 
 * Each change is an **operation** (create, update, delete or move an
-  object, or change the settings), kept as the API received it.
+  object, or change the settings), kept as the API received it. A move
+  staged right after a move of the same object takes its place: moving a
+  rule up three steps is one operation, and moving it back where it was
+  takes it out.
 * Staged in a changeset, an operation is checked as it is added: the
   changeset with it must still be valid, and nftables must accept the
   ruleset it makes. Nothing is applied.