* perf: preserve matching Accounts settings sections during search
* refactor(settings): route Accounts' section stack through SettingsSectionStack
Replaces the pane-local index-keyed wrapper with the shared SettingsSectionStack so the
search-stable identity rule lives in one place, and restates the read/subscription-count
oracles as node identity plus non-growing counts so a future freshness fix cannot read as
a regression. Applied on the branch head; the rebase onto main is still outstanding.