Add nodeToXPath() to core — builds a unique XPath selector for any node
by walking up the tree and using name predicates (or positional index
when names collide among same-type siblings). Properly escapes names
containing quotes using XPath concat() or double-quote delimiters.
UI: "Copy node ID" and "Copy XPath" items in the canvas right-click
"Copy/Paste as" submenu. Also i18n the entire submenu — all labels now
use menuMessages with translations for de, es, fr, it, pl, ru, zh-CN.
CLI: `open-pencil selection` command (app-mode only) returns selected
nodes with id, name, type, size, and xpath. Connects to the running
app via the automation WebSocket.
Automation: new `selection` RPC handler that returns selected nodes
with computed XPath selectors.
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