moveCursor() repositioned the cursor but never called updateAutocomplete()
or cancelAutocomplete(), unlike insertCharacter()/handleBackspace(). So an
open autocomplete picker went stale when the cursor moved: e.g. typing
`/cmd ` (argument menu open) then arrowing Left back into the command name
left the argument list showing against a `/cmd` prefix, and a Tab there
concatenated the stale suggestion onto the partial command name
(e.g. `/swarepo`).
Sync the picker at the end of moveCursor(): when a picker is open, re-query
via updateAutocomplete(), which refreshes the list for the new cursor
position or closes it when nothing matches.
Adds a regression test in test/editor.test.ts (verified to fail without the
fix). Fixesearendil-works/pi#5496.