The inline "Delete location" action was the last spot on the Backup
page still using the native browser confirm() — the snapshot delete
already uses the styled backup-modal, so the location delete sat out
as the odd one. Adds a new #backup-delete-location-modal matching the
existing modal shell (header / body / backup-danger-btn footer),
swaps deleteInlineLocation() to open it instead of confirm(), and
wires the confirm button to a new confirmDeleteLocation() that does
the actual `libreportal backup location remove <idx>` task.
Behaviour is the same — confirm body text moves into the modal as a
muted hint paragraph using backup-card-hint, location name bolded
for scannability. expandedLocs cleanup also moves into the confirm
handler so the row collapses only when the user actually deletes.
Signed-off-by: librelad <librelad@digitalangels.vip>