Trigger editor re-render after page metadata is loaded to ensure Lua
widgets re-evaluate with the correct context. This fixes issue #1729
where widgets would show broken state on initial page load because
ctx.currentPage would be nil until the metadata finished loading
asynchronously.
The fix dispatches an empty CodeMirror transaction after updating the
page metadata, which triggers all decorator state fields (including
Lua widgets) to re-render with the updated metadata.
