Puts the stepped engine behind the "34 available" chip so it is not
CLI-only. Wired end to end: updater_upgrade task type -> task-router ->
updaterUpgrade action -> `libreportal updater upgrade <app> [version]`,
with a label and icon in the tasks list.
The button always confirms, and the dialog states the plan and the
guarantee rather than asking "are you sure?" — which app, from which
version to which, that every step snapshots first and waits for the app
to confirm it is serving with no migration outstanding, that a failure
stops the ladder on the last version that verified, and that it can take
a long time because each release runs its own migration.
Both delegated dispatchers (per-app Updates tab and the fleet Overview
rows) learn the action, so the button works wherever the chip appears.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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