Plasma's Apply writes every cfg_* value of the current page. General and
Popup both hold the hidden usage rows and detail sections, loaded when
the page opened, so applying any setting on either page rewrote those
lists and undid rows or sections hidden or restored in the popup
meanwhile.

Both pages now follow the stored lists while keeping their own pending
restores: a new ConfigValueSync rule drops the items the page restored
from the latest stored list and adopts every other change. Tests run the
real page handlers and restores for both pages.

Documentation impact: CHANGELOG Unreleased and the usage guide's hidden
items entry. TODO.md is unaffected.

Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>