Grafana served no dashboards: only datasources were provisioned, while
the module header already claimed dashboards were. This ships the agents
dashboard as a file provider and makes that sentence true.
The datasource uid is bound once and substituted into the dashboard at
build time. Committing the literal would make the dashboard a second
speller of a name the datasource already owns, and the drift failure is
silent -- panels render empty rather than erroring.
The shipped copy drops the `DS` datasource variable: it exists so an
operator can pick a store on manual import, and a provisioned dashboard
must not ask.
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