Adds a Tabler-icon badge in the stacked-note action bar showing whether
the loaded copy still matches GitHub HEAD (verified / outdated / offline
/ checking / unknown / stale-known). The save flow now re-checks before
the PUT and opens a conflict modal when GitHub has moved on, with three
explicit choices: discard local edits and pull, overwrite anyway, or
cancel. Race-condition 409s from the PUT itself are routed through the
same modal.
