Live undo/redo: add/delete component and link, move, property edits

Undo and redo now work against a connected device; each step is sent
there through Sox. Deleting a component first reads its whole subtree
back (config, unloaded children, links, place among siblings) so undo
can recreate it; recreated components take new device ids, which the
DOM elements pick up so later steps still reach them. Binary Buf
config (a user's cred) is read with read_prop, since the cache decodes
every Buf as a Str. Moves, tidy layout, and Properties / page editor /
user edits record only what the device accepted.

A step that does not fully reach the device warns and clears the
history. History is also cleared on every view change in live mode,
as opening a sheet rebuilds the DOM from the device.

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

user_service_view.py

@@ -485,12 +485,17 @@ class _UserDialog:
 
         if app_state.live_mode:
             failures = []
-            for elem, prop, _old, new in changes:
+            applied = []
+            for change in changes:
+                elem, prop, _old, new = change
                 if live_hooks.live_set_prop_value(elem, prop, new):
                     set_prop_value(elem, prop, new)
+                    applied.append(change)
                     app_state.mark_dirty()
                 else:
                     failures.append(f"{prop}: {live_hooks.last_error}")
+            if applied:
+                undo.push(undo.LiveSlotValueCommand(applied, label="edit user"))
             if failures:
                 live_hooks.warn_failure(
                     "Edit User",