Replace the JobsTab stub with a real implementation on the backups
service page, lifted from components/BackupsPage.tsx. Renders the
Jobs/Runs/Alerts sub-tabs with their existing tables
(BackupJobsTable, BackupRunsTable, BackupAlertsTable) and the
acknowledge-alert mutation.
The backup hooks (useBackupJobs/Runs/Alerts) currently query globally --
the backend gained service_id attribution in slice 3, but the hooks
don't yet accept a serviceId param. This tab shows all backups data for
now; per-instance scoping by instance.id is a documented follow-up once
the hooks gain the parameter.
The page heading from BackupsPage is dropped (the service page header
already shows the instance name + 'Backups' binding).
stubs.tsx loses the JobsTab stub; index.ts wires the real component.
Tests: JobsTab renders sub-tabs + job-name rows with mocked hooks. 96
tests pass (+2); lint/build green.
Refs openspec/changes/services-as-hub-ia/ (spec R2.4, tasks slice 7).
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